Method of forming multi-layer sintering object support structure

ABSTRACT

Support substrates are used in certain additive fabrication processes to permit processing of an object. For additive fabrication processes with materials that are sintered into a final part, a multi-layer support substrate of interleaved support and interface layers is fabricated to support an object while reducing an impact of friction on shrinkage of the part during the sintering process.

RELATED APPLICATIONS

This application is related to the following patent applications: Int'lPat. App. No. PCT/US17/24067 filed on Mar. 24, 2017; Int'l Pat. App. No.PCT/US17/20817 filed on Mar. 3, 2017; U.S. patent application Ser. No.15/059,256 filed on Mar. 2, 2016; U.S. patent application Ser. No.15/245,702 filed on Aug. 24, 2016; and U.S. patent application Ser. No.15/382,535 filed on Dec. 16, 2016. This application is also related tothe following U.S. provisional patent applications: U.S. Prov. Pat. App.No. 62/303,310 filed on Mar. 3, 2016, U.S. Prov. Pat. App. No.62/303,341 filed on Mar. 3, 2016, U.S. Prov. Pat. App. No. 62/434,014filed on Dec. 14, 2016, U.S. Prov. Pat. App. No. 62/421,716 filed onNov. 14, 2016, U.S. Prov. Pat. App. No. 62/461,726 filed on Feb. 21,2107, U.S. Prov. Pat. App. No. 62/322,760 filed on Apr. 14, 2016, U.S.Prov. Pat. App. No. 62/432,298 filed on Dec. 9, 2016, and U.S. Prov.Pat. App. No. 62/473,372 filed on Mar. 18, 2017. Each of the foregoingapplications is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The systems and methods described herein relate to additivemanufacturing, and more specifically to techniques for fabricatingsupport structures, breakaway layers, and the like suitable for use withsinterable build materials.

BACKGROUND

Support structures are commonly used in additive manufacturing to expandthe features available in fabricated object, e.g., by providingunderlying structural support for overhangs or lengthy bridges ofotherwise unsupported material. However, when additively manufacturingwith materials that require additional processing such as debinding andsintering to form a final part, conventional support strategies andtechniques may fail on multiple fronts, such as where support structuresdeform or shrink in patterns that do not match the supported object orwhere support structures sinter together with the supported object toform a single, inseparable structure. There remains a need for supporttechniques, materials, and strategies suitable for use with additivelymanufactured, sinterable objects.

SUMMARY

Support structures are used in certain additive fabrication processes topermit fabrication of a greater range of object geometries. For additivefabrication processes with materials that are subsequently sintered intoa final part, an interface layer is fabricated between the object andsupport in order to inhibit bonding between adjacent surfaces of thesupport structure and the object during sintering.

In an aspect of the sintering method and systems described herein asintering structure may include an object fabricated from a firstmaterial with a three-dimensional printer according to athree-dimensional model. The first material may include a sinterablepowder and a binder to retain a shape of the object during processinginto a final part. The sintering structure may further include aplurality of sinterable layers having a sintering shrink rate matched tothe first material. The sintering structure may further include aplurality of interface layers that resists sintering at a sinteringtemperature for the sinterable powder of the first material, thesinterable layers and the interface layers may be layered in analternating pattern to form a vertical stack. At least one of theinterface layers may be disposed between two of the sinterable layers inthe vertical stack and at least one other of the interface layers may bedisposed between an uppermost layer of the sinterable layers and theobject.

In the aspect, each of the interface layers may include a materialhaving a different composition than the first material. Also, in theaspect, each of the interface layers may resist bonding to adjacent onesof the sinterable layers during sintering. At least one of the interfacelayers may include a material that has a different composition than atleast one other one of the interface layers. At least one of thesinterable layers may include a material that has a differentcomposition than at least one other one of the sinterable layers.Further in the aspect, at least one of interface layers may comprise aceramic powder with a sintering temperature substantially higher thanthe sintering temperature of the sinterable powder. The sinterablelayers and the interface layers may be substantially parallel. In theaspect, a perimeter of at least one of the sinterable layers may bederived from a projected convex hull of the object. Additionally, thevertical stack may include a network of open passages to facilitatedrainage of a debinding solution from the structure. Further in theaspect, at least one of the sinterable layers may be at least threetimes as thick as adjacent ones of the interface layers.

In another aspect of the sintering methods and systems described herein,a method of forming a multi-layer shrink rate-isolating substrate mayinclude providing a base layer including a powered material that sintersat a sintering temperature and a first binder system that retains afirst shape of the base layer; fabricating a first interface layer abovethe base layer, the first interface layer including an interfacematerial that resists sintering during thermal processing at thesintering temperature; fabricating a support layer above the firstinterface layer from a material sinterable at the sintering temperature;depositing a second interface layer above the support layer, the secondinterface layer including the interface material; and fabricating anobject from a build material above the second interface layer, the buildmaterial including a powdered metal that sinters at the sinteringtemperature and a second binder system that retains a second shape ofthe object during processing of the object into a final part. In thisaspect, the build material may have a substantially similar compositionto at least one of the base layer and the support layer. The buildmaterial may also have a substantially similar sintering shrinkage rateto at least one of the base layer and the support layer. The firstinterface layer and the second interface layer may reduce to a powderduring thermal processing at the sintering temperature. In the aspect,the first interface layer may resist bonding of the base layer to thesupport layer during thermal processing at the sintering temperature.Additionally, the second interface layer may resist bonding of thesupport layer to the object during thermal processing at the sinteringtemperature. Further in the aspect, the interface material may include aceramic powder with a second sintering temperature substantially greaterthan the sintering temperature of the build material. The method mayfurther include fabricating one or more additional support layers andone or more additional interface layers between the base layer and theobject.

In yet another aspect of the sintering methods and systems describedherein, a structure may include a plurality of support layers formed ofa first material that may include a powdered material that sinters at asintering temperature into a densified layer that shrinks at a firstrate during sintering. The structure may further include a plurality ofinterface layers. Each of the interface layers may be formed between twoadjacent support layers. In addition, each of the interface layers maybe formed of a second material that prevents bonding between the supportlayers during thermal processing at the sintering temperature. Thestructure may further include a top layer of the structure that may bemade of a layer of the second material. The structure may furtherinclude an object disposed on the top layer. The object may be shaped bya three-dimensional printer according to a three-dimensional model ofthe object. The object may also be formed by the three-dimensionalprinter of a material that sinters during thermal processing at thesintering temperature.

The method may include applying pressure to collapse the microspheres,the collapse of the microspheres separating the support structure fromthe object. The interface layer may be formed of the first material.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the devices,systems, and methods described herein will be apparent from thefollowing description of particular embodiments thereof, as illustratedin the accompanying drawings. The drawings are not necessarily to scale,emphasis instead being placed upon illustrating the principles of thedevices, systems, and methods described herein.

FIG. 1 shows an additive manufacturing system for use with sinterablebuild materials.

FIG. 2 shows a flow chart of a method for additive fabrication withsinterable build materials.

FIG. 3 shows an additive manufacturing system using fused filamentfabrication.

FIG. 4 shows an additive manufacturing system using binder jetting.

FIG. 5 shows a stereolithography system.

FIG. 6 shows a stereolithography system.

FIG. 7 shows an interface layer.

FIG. 8 shows a flow chart of a method for forming an interface layer forremovable supports.

FIG. 9 shows a flow chart of a method for fabricating an object withoverhead supports.

FIG. 10 shows an object with overhead support.

FIG. 11 shows a cross-section of an object on a shrinking substrate.

FIG. 12 shows a top view of an object on a shrinking substrate.

FIG. 13 is a flowchart of a method for fabricating shrinkable supportstructures.

FIG. 14 shows a flow chart of a method for independently fabricatingobjects and object supports.

FIG. 15 shows a flow chart of a method for fabricating multi-partassemblies.

FIG. 16 illustrates a mechanical assembly in a casing.

FIG. 17 shows a flow chart of a method for fabricating removable sintersupports.

FIG. 18 shows a flow chart of a method for forming an interface layer ina binder jetting process.

FIG. 19 shows a flow chart of a method for forming a multi-layersintering object support substrate.

FIG. 20 shows a side view of a multi-layer structure for sintering anobject.

FIG. 21 shows a side view of an alternate embodiment of a multi-layerstructure for sintering an object.

DETAILED DESCRIPTION

Embodiments will now be described with reference to the accompanyingfigures.

The foregoing may, however, be embodied in many different forms andshould not be construed as limited to the illustrated embodiments setforth herein.

All documents mentioned herein are hereby incorporated by reference intheir entirety. References to items in the singular should be understoodto include items in the plural, and vice versa, unless explicitly statedotherwise or clear from the text. Grammatical conjunctions are intendedto express any and all disjunctive and conjunctive combinations ofconjoined clauses, sentences, words, and the like, unless otherwisestated or clear from the context. Thus, the term “or” should generallybe understood to mean “and/or” and so forth.

Recitation of ranges of values herein are not intended to be limiting,referring instead individually to any and all values falling within therange, unless otherwise indicated herein, and each separate value withinsuch a range is incorporated into the specification as if it wereindividually recited herein. The words “about,” “approximately” or thelike, when accompanying a numerical value, are to be construed asindicating a deviation as would be appreciated by one of ordinary skillin the art to operate satisfactorily for an intended purpose. Similarly,words of approximation such as “approximately” or “substantially” whenused in reference to physical characteristics, should be understood tocontemplate a range of deviations that would be appreciated by one ofordinary skill in the art to operate satisfactorily for a correspondinguse, function, purpose, or the like. Ranges of values and/or numericvalues are provided herein as examples only, and do not constitute alimitation on the scope of the described embodiments. Where ranges ofvalues are provided, they are also intended to include each value withinthe range as if set forth individually, unless expressly stated to thecontrary. The use of any and all examples, or exemplary language(“e.g.,” “such as,” or the like) provided herein, is intended merely tobetter illuminate the embodiments and does not pose a limitation on thescope of the embodiments. No language in the specification should beconstrued as indicating any unclaimed element as essential to thepractice of the embodiments.

In the following description, it is understood that terms such as“first,” “second,” “top,” “bottom,” “up,” “down,” and the like, arewords of convenience and are not to be construed as limiting termsunless specifically stated to the contrary.

FIG. 1 shows an additive manufacturing system for use with sinterablebuild materials. The system 100 may include a printer 102, a conveyor104, and a post-processing station 106.

In general, the printer 102 may be any of the printers described hereinor any other three-dimensional printer suitable for adaptation tofabrication with sinterable build materials. By way of non-limitingexample, the printer 102 may include a fused filament fabricationsystem, a binder jetting system, a stereolithography system, a selectivelaser sintering system, or any other system that can be usefully adaptedto form a net shape object under computer control using the sinterablebuild materials contemplated herein.

The output of the printer 102 may be an object 103 that is a green bodyor the like formed of a build material including any suitable powder(e.g., metal, metal alloy, ceramic, and so forth, as well ascombinations of the foregoing), along with a binder that retains thepowder in a net shape produced by the printer 102. A wide range ofcompositions may be employed as the build material contemplated herein.For example, powdered metallurgy materials or the like may be adaptedfor use as a build material in a fused filament fabrication process orthe like. Metal injection molding materials with suitablethermo-mechanical properties for extrusion in a fused filamentfabrication process are described by way of non-limiting example inHeaney, Donald F., ed. “Handbook of Metal Injection Molding” (2012), theentire contents of which are hereby incorporated by reference.

The conveyor 104 may be used to transport the object 103 from theprinter 102 to a post-processing station 106, which may include one ormore separate processing stations, where debinding and sintering can beperformed. The conveyor 104 may be any suitable mechanism or combinationof devices suitable for physically transporting the object 103. Thismay, for example, include robotics and a machine vision system or thelike on the printer side for detaching the object 103 from a buildplatform, as well as robotics and a machine vision system or the like onthe post-processing side to accurately place the object 103 within thepost-processing station 106. In another aspect, the post-processingstation 106 may serve multiple printers so that a number of objects canbe debound and sintered concurrently, and the conveyor 104 mayinterconnect the printers and post-processing station so that multipleprint jobs can be coordinated and automatically completed in parallel.In another aspect, the object 103 may be manually transported betweenthe two corresponding stations.

The post-processing station 106 may be any system or combination ofsystems useful for converting a green part formed into a desired netshape from a metal injection molding build material by the printer 102into a final object. The post-processing station 106 may, for example,include a debinding station such as a chemical debinding station fordissolving binder materials in a solvent or the like, or more generallyany debinding station configured to remove at least a portion of thebinder system from the build material of the object 103. Thepost-processing station 106 may also or instead include a thermalsintering station for applying a thermal sintering cycle at a sinteringtemperature for the build material, or the powdered material in thebuild material, such as a sintering furnace configured to sinter thepowdered material into a densified object. The components of thepost-processing station 106 may be used in sequence to produce a finalobject. As another example, some contemporary injection moldingmaterials are engineered for thermal debinding, which makes it possibleto perform a combination of debinding and sintering steps with a singleoven or similar device. In general, the thermal specifications of asintering furnace will depend upon the powdered material, the bindersystem, the volume loading of the powdered material into the bindersystem, and other aspects of the green object and the materials used tomanufacture same. Commercially available sintering furnaces forthermally debound and sintered metal injection molding (MIM) parts willtypically operate with an accuracy of +/−5 degrees Celsius or better,and at temperatures of at least 600 degrees Celsius, or from about 200degrees Celsius to about 1900 degrees Celsius for extended times. Anysuch furnace or similar heating device may be usefully employed as thepost-processing station 106 as contemplated herein. Vacuum or pressuretreatment may also or instead be used. In an aspect, after the object103 is placed in the oven, beads of an identical or similar composition,with the addition of an unsinterable exterior coating, may be packedinto the oven with the object to provide general mechanical support witha thermally matched shrinkage rate that will not form a bond to theobject during sintering.

In the context of this description, it will be appreciated thatsintering may usefully include different types of sintering. Forexample, sintering may include the application of heat to sinter anobject to full density or nearly full density. In another aspect,sintering may include partial sintering, e.g., for a sintering andinfiltration process in which pores of a partially sintered part arefilled, e.g., through contact and capillary action, with some othermaterial such as a low melting point metal to increase hardness,increase tensile strength, or otherwise alter or improve properties of afinal part. Thus, any references herein to sintering should beunderstood to contemplate sintering and infiltration unless a differentmeaning is expressly stated or otherwise clear from the context.Similarly, references to a sinterable powder or sinterable buildmaterial should be understood to contemplate any sinterable materialincluding powders that can be sintered and infiltrated to form a finalpart.

It should also be understood that, where an infiltrable build materialis used, the corresponding interface layer should be engineered toresist any infiltration that might result in the formation of amechanical bond across the barrier created by the interface layer. Thus,for example, when using infiltrable build materials, a powdered materialsuch as a ceramic of the interface layer may usefully have a particlesize and shape selected to be substantially resistant to infiltration bythe infiltrant (e.g., an infiltrating liquid) used to densify theobject. While the infiltration barrier may be created mechanically basedon shape and size of particles, e.g., by creating particles that arevery small to slow the wicking of a liquid infiltrant into the interfacelayer, the barrier may also or instead be created chemically by coatingparticles with, or forming the particles from, a substantiallynon-wetting material relative to the infiltrating liquid. These and anyother techniques that would be apparent to one of ordinary skill in theart may be used to create an interface layer for use with infiltrablebuild materials as contemplated herein.

It will also be appreciated that a wide range of other debinding andsintering processes can be used. For example, the binder may be removedin a chemical debind, thermal debind, or some combination of these.Other debinding processes are also known in the art, such assupercritical debinding or catalytic debinding, any of which may also orinstead be employed by the post-processing station 106. For example, ina common process, a green part is first debound using a chemical debind,which is following by a thermal debind at a moderately high temperature(in this context, around 700-800 Celsius) to remove organic binder andcreate enough necks among a powdered material to provide sufficientstrength for handling. From this stage, the object may be moved to asintering furnace to remove any remaining components of a binder systemand densify the object into a final part. In another aspect, a purethermal debind may be used to remove the organic binder. More generally,any technique or combination of techniques may be usefully employed todebind an object as contemplated herein.

Similarly, a wide range of sintering techniques may be usefully employedby the post-processing station 106. In one aspect, an object may beconsolidated in a furnace to a high theoretical density using vacuumsintering. In another aspect, the furnace may use a combination offlowing gas (e.g., at below atmosphere, slightly above atmosphere, orsome other suitable pressure) and vacuum sintering. More generally, anysintering or other process suitable for improving object density may beused, preferably where the process yields a near-theoretical densitypart with little or no porosity. Hot-isostatic pressing (“HIP”) may alsoor instead be employed, e.g., by applying elevated temperatures andpressures of 10-50 ksi, or between about 15 and 30 ksi, as apost-sintering step to increase density of the final part. In anotheraspect, the object may be processed using any of the foregoing, followedby a moderate overpressure (greater than the sintering pressure, butlower than HIP pressures). In this latter process, gas may bepressurized at 100-1500 psi and maintained at elevated temperatureswithin the furnace or some other supplemental chamber. In anotheraspect, the object may be separately heated in one furnace, and thenimmersed in a hot granular media inside a die, with pressure applied tothe media so that it can be transmitted to the object to drive morerapid consolidation to near full density. More generally, any techniqueor combination of techniques suitable for removing binder systems anddriving a powdered material toward consolidation and densification maybe used by the post-processing station 106 to process a fabricated greenpart as contemplated herein.

In one aspect, the post-processing station 106 may be incorporated intothe printer 102, thus removing a need for a conveyor 104 to physicallytransport the object 103. The build volume of the printer 102 andcomponents therein may be fabricated to withstand the elevateddebinding/sintering temperatures. In another aspect, the printer 102 mayprovide movable walls, barriers, or other enclosure(s) within the buildvolume so that the debind and/or sinter can be performed while theobject 103 is on a build platform within the printer 102, but thermallyisolated from any thermally sensitive components or materials.

The post-processing station 106 may be optimized in a variety of waysfor use in an office environment. In one aspect, the post-processingstation 106 may include an inert gas source 108. The inert gas source108 may, for example, include argon or other inert gas (or other gasthat is inert to the sintered material), and may be housed in aremovable and replaceable cartridge that can be coupled to thepost-processing station 106 for discharge into the interior of thepost-processing station 106, and then removed and replaced when thecontents are exhausted. The post-processing station 106 may also orinstead include a filter 110 such as a charcoal filter or the like forexhausting gasses that can be outgassed into an office environment in anunfiltered form. For other gasses, an exterior exhaust, or a gascontainer or the like may be provided to permit use in unventilatedareas. For reclaimable materials, a closed system may also or instead beused, particularly where the environmental materials are expensive ordangerous.

In one aspect, the post-processing station 106 may be coupled to othersystem components. For example, the post-processing station 106 mayinclude information from the printer 102, or from a controller for theprinter, about the geometry, size, mass, and other physicalcharacteristics of the object 103 in order to generate a suitabledebinding and sintering profile. In another aspect, the profile may beindependently created by the controller or other resource andtransmitted to the post-processing station 106 when the object 103 isconveyed. In another aspect, the post-processing station 106 may monitorthe debinding and sintering process and provide feedback, e.g., to asmart phone or other remote device 112, about a status of the object103, a time to completion, and other processing metrics and information.The post-processing station 106 may include a camera 114 or othermonitoring device to provide feedback to the remote device 112, and mayprovide time lapse animation or the like to graphically show sinteringon a compressed time scale. Post-processing may also or instead includefinishing with heat, a hot knife, tools, or similar. Post-processing mayinclude applying a finish coat.

In another aspect, the post-processing station 106 may be remote fromthe printer 102, e.g., in a service bureau model or the like where theobject 103 is fabricated and then sent to a service bureau foroutsourced debinding, sintering and so forth. Thus, for any of thesupport structures, interface layers, and so forth described below, ormore generally, for any fabricated items described below, thisdisclosure expressly contemplates a corresponding method of receiving anobject or item containing any such features, e.g., any features orstructures described below, and then performing one or morepost-processing steps including but not limited to shaping, debinding,sintering, finishing, assembly, and so forth. This may, for example,include receiving a green part with a fully intact binder system, at aremote processing resource, where the part can be debound and sinteredat the remote processing resource. This may also or instead includereceiving a brown part where some or all of the binder system has beenremoved in a debinding process at another location and the part is onlysintered at the remote processing resource. In this latter case, aportion of the binder system may usefully be retained in the part,either as a backbone binder to retain a shape of the object duringsintering until a self-supporting sintering strength is achieved, or asa residual primary binder that is left in the part to improve structuralintegrity during shipping or other handling.

More generally, this disclosure contemplates any combination anddistribution of steps suitable for centralized or distributed processinginto a final part, as well as any intermediate forms of the materials,articles of manufacture, and assemblies that might be used therein.

For example, in one aspect, a method disclosed herein may includereceiving an article from a creator at a remote processing resource suchas a service bureau, sintering service, or the like. The article mayinclude a support structure fabricated from a first material, aninterface layer adjacent to the support structure, and an objectsupported by the support structure and fabricated from a secondmaterial, the object having a surface adjacent to the interface layer,where the second material includes a powdered material for forming afinal part and a binder system including one or more binders, where theone or more binders retain a net shape of the object during processingof the object into the final part, where processing of the object intothe final part includes debinding the net shape to remove at least aportion of the one or more binders and sintering the net shape to joinand densify the powdered material, and where the interface layer resistsbonding of the support structure to the object during sintering. Thearticle may have been fabricated, for example, at another facility withan additive fabrication system but no sintering (and/or debinding)resources. The method may include processing the article at the remoteprocessing resource into the final part, where processing the articleincludes at least one of debinding the article and sintering thearticle, and where processing the article further includes separatingthe object from the support structure at the interface layer. Theresulting article may then be returned to the creator for any intendeduse.

FIG. 2 shows a method for fabricating an object. The method 200 is morespecifically a generalized method for layer-by-layer fabrication of anobject using sinterable materials.

As shown in step 202, the method 200 may begin with providing a materialfor fabrication. This may include any of a variety of materials that canbe usefully handled in a layer-based fabrication process such as fusedfilament fabrication, binder jetting, stereolithography, and so forth. Anumber of suitable materials are discussed in greater detail below. Moregenerally, any material mentioned herein that is suitable for use in alayer-based fabrication system may be employed as the material in thismethod 200. It will further be appreciated that other techniques thatare not layer based, including subtractive techniques such as milling orfluid jetting, may also or instead be used, and any correspondinglysuitable materials may also or instead be employed as a build materialfor fabricating an object.

Furthermore, additional materials may be employed by a fabricationsystem, such as support materials, interface layers, finishing materials(for exterior surfaces of an object) and so forth, any of which may beused as a material for fabrication in the systems and methodscontemplated herein.

As shown in step 204, the method may include fabricating a layer for anobject. This may, for example, include a layer of the object itself or alayer of a support structure. For a particular layer (e.g., at aparticular z-axis position of a fabrication system), an interface layermay also or instead be fabricated to provide a non-sinterable interfaceor similar release layer or structure between a support structure (or asubstrate such as a raft, setter, or print bed) and an object. Inanother aspect, finishing materials for exterior surfaces may be used,such as materials that impart desired aesthetic, structural, orfunctional properties to surfaces of the object.

As shown in step 210, a determination may be made whether the object(and related supports, etc.) is complete. If the object is not complete,the method 200 may return to step 204 and another layer may befabricated. If the object is complete, then the method 200 may proceedto step 212 where post-processing begins.

As shown in step 212, the method 200 may include shaping the object.Prior to debinding and sintering, an object is typically in a softer,more workable state. While this so-called green part is potentiallyfragile and subject to fracturing or the like, the more workable stateaffords a good opportunity for surface finishing, e.g., by sanding orotherwise smoothing away striations or other artifacts of thelayer-based fabrication process, as well as spurs, burrs and othersurface defects that deviate from a computerized model of an intendedshape of the object. In this context, shaping may include manualshaping, or automated shaping using, e.g., a computerized millingmachine, grinding tools, or a variety of brushes, abrasives and so forthor any other generally subtractive technique or tool(s). In one aspect,a fluid stream of a gas such as carbon dioxide may be used to carry dryice particulates to smooth or otherwise shape a surface. In this latterapproach, the abrasive (dry ice) can conveniently change phase directlyto a gas under normal conditions, thus mitigating cleanup of abrasivesafter shaping the object.

As shown in step 214, the process 200 may include debinding the printedobject. In general, debinding may remove some or all of a binder orbinder system that retains a build material containing a metal (orceramic or other) powder in a net shape that was imparted by theprinter. Numerous debinding techniques, and corresponding bindersystems, are known in the art and may be used as binders in the buildmaterials contemplated herein. By way of non-limiting examples, thedebinding techniques may include thermal debinding, chemical debinding,catalytic debinding, supercritical debinding, evaporation and so forth.In one aspect, injection molding materials may be used. For example,some injection molding materials with rheological properties suitablefor use in a fused filament fabrication process are engineered forthermal debinding, which advantageously permits debinding and sinteringto be performed in a single baking operation, or in two similar bakingoperations. In another aspect, many binder systems may be quickly andusefully removed in a debinding process by microwaving an object in amicrowave oven or otherwise applying energy that selectively removesbinder system from a green part. With a suitably adapted debindingprocess, the binder system may include a single binder, such as a binderthat is removable through a pure thermal debind.

More generally, the debinding process removes a binder or binder systemfrom a net shape green object, thus leaving a dense structure of metal(or ceramic or other) particles, generally referred to as a brown part,that can be sintered into the final form. Any materials and techniquessuitable for such a process may also or instead be employed fordebinding as contemplated herein.

As shown in step 216, the process 200 may include sintering the printedand debound object into a final form. In general, sintering may includeany process of densifying and forming a solid mass of material byheating without liquefaction. During a sintering process, necks formbetween discrete particles of a material, and atoms can diffuse acrossparticle boundaries to fuse into a solid piece. Because sintering can beperformed at temperatures below the melting temperature, thisadvantageously permits fabrication with very high melting pointmaterials such as tungsten and molybdenum.

Numerous sintering techniques are known in the art, and the selection ofa particular technique may depend upon the build material used, the sizeand composition of particles in a material and the desired structural,functional or aesthetic result for the fabricated object. For example,in solid-state (non-activated) sintering, metal powder particles areheated to form connections (or “necks”) where they are in contact. Overa thermal sintering cycle, these necks can thicken and create a densepart, leaving small, interstitial voids that can be closed, e.g., by hotisostatic pressing (HIP) or similar processes. Other techniques may alsoor instead be employed. For example, solid state activated sinteringuses a film between powder particles to improve mobility of atomsbetween particles and accelerate the formation and thickening of necks.As another example, liquid phase sintering may be used, in which aliquid forms around metal particles. This can improve diffusion andjoining between particles, but also may leave lower-melting phase withinthe sintered object that impairs structural integrity. Other advancedtechniques such as nano-phase separation sintering may be used, forexample to form a high-diffusivity solid at the necks to improve thetransport of metal atoms at the contact point, as described for examplein “Accelerated sintering in phase-separating nanostructured alloys,”Park et al., Nat. Commun. 6:6858 (2015) (DOI: 10.1038/ncomms7858).Sintering may also or instead include partial sintering into a porousarticle that can be infiltrated with another material to form a finalpart.

It will be understood that debinding and sintering result in materialloss and compaction, and the resulting object may be significantlysmaller than the printed object. However, these effects are generallylinear in the aggregate, and net shape objects can be usefully scaled upwhen printing to create a shape with predictable dimensions afterdebinding and sintering. Additionally, as noted above, it should beappreciated that the method 200 may include sending a fabricated objectto a processing facility such as a service bureau or other remote oroutsourced facility, and the method 200 may also or instead includereceiving the fabricated object at the processing facility andperforming any one or more of the post-fabrication steps described abovesuch as the shaping of step 212, the debinding of step 214, or thesintering of step 216.

FIG. 3 is a block diagram of an additive manufacturing system. Theadditive manufacturing system 300 shown in the figure may, for example,include a fused filament fabrication additive manufacturing system, orany other additive manufacturing system or combination of manufacturingsystems including a printer 301 that deposits a build material 302according to a computerized model to form an object, along with anyrelated support structures, interface layers, and so forth. While theprinter 301 is generally intended for use with sinterable buildmaterials, the additive manufacturing system 300 may also or instead beused with other build materials including plastics, ceramics, and thelike, as well as other materials such as interface layers, supportstructures and the like that do not sinter to form a final part.

In one aspect, the printer 301 may include a build material 302 that ispropelled by a drive system 304 and heated to an extrudable state by aheating system 306, and then extruded through one or more nozzles 310.By concurrently controlling robotics 308 to position the nozzle(s) alongan extrusion path relative to a build plate 314, an object 312 may befabricated on the build plate 314 within a build chamber 316. Ingeneral, a control system 318 may manage operation of the printer 301 tofabricate the object 312 according to a three-dimensional model using afused filament fabrication process or the like.

A printer 301 disclosed herein may include a first nozzle for extrudinga first material. The printer 301 may also include a second nozzle forextruding a second material, where the second material has asupplemental function (e.g., as a support material or structure) orprovides a second build material with different mechanical, functional,or aesthetic properties useful for fabricating a multi-material object.The second material may be reinforced, for example, with an additivesuch that the second material has sufficient tensile strength orrigidity at an extrusion temperature to maintain a structural pathbetween the second nozzle and a solidified portion of an object duringan unsupported bridging operation. Other materials may also or insteadbe used as a second material. For example, this may include thermallymatched polymers for fill, support, separation layers, or the like. Inanother aspect, this may include support materials such as water-solublesupport materials with high melting temperatures at or near the windowfor extruding the first material. Useful dissolvable materials mayinclude a salt or any other water-soluble material(s) with suitablethermal and mechanical properties for extrusion as contemplated herein.In another aspect, a second (or third, or fourth . . . ) nozzle may beused to introduce an infiltrating material to modify properties ofanother deposited material, e.g., to strength a material, stabilize anexterior finish, etc. While a printer 301 may usefully include twonozzles, it will be understood that the printer 301 may more generallyincorporate any practical number of nozzles, such as three or fournozzles, according to the number of materials necessary or useful for aparticular fabrication process.

The build material 302 may be provided in a variety of form factorsincluding, without limitation, any of the form factors described hereinor in materials incorporated by reference herein. The build material 302may be provided, for example, from a hermetically sealed container orthe like (e.g., to mitigate passivation), as a continuous feed (e.g., awire), or as discrete objects such as rods or rectangular prisms thatcan be fed into a chamber or the like as each prior discrete unit ofbuild material 302 is heated and extruded. In one aspect, the buildmaterial 302 may include an additive such as fibers of carbon, glass,Kevlar, boron silica, graphite, quartz, or any other material that canenhance tensile strength of an extruded line of material. In one aspect,the additive(s) may be used to increase strength of a printed object. Inanother aspect, the additive(s) may be used to extend bridgingcapabilities by maintaining a structural path between the nozzle and acooled, rigid portion of an object being fabricated. In one aspect, twobuild materials 302 may be used concurrently, e.g., through twodifferent nozzles, where one nozzle is used for general fabrication andanother nozzle is used for bridging, supports, or similar features.

In an aspect, the build material 302 may be fed (one by one) as billetsor other discrete units into an intermediate chamber for delivery intothe build chamber 316 and subsequent heating and deposition. Wherefabrication is performed in a vacuum or other controlled environment,the build material 302 may also or instead be provided in a cartridge orthe like with a vacuum environment (or other controlled environment)that can be directly or indirectly coupled to a corresponding controlledenvironment of the build chamber 316. In another aspect, a continuousfeed of the build material 302, e.g., a wire or the like, may be fedthrough a vacuum gasket into the build chamber 316 in a continuousfashion, where the vacuum gasket (or any similar fluidic seal) permitsentry of the build material 302 into the chamber 316 while maintaining acontrolled build environment inside the chamber 316.

In another aspect, the build material 302 may be provided as a supply ofpreformed blocks 303, and the robotics 308 may include a second roboticsystem configured to position on or more of the preformed blocks to forman interior structure within the object 312. This may be useful, forexample, to quickly build volumes of a relatively large object that donot require shaping of exterior surfaces.

The build material 302 may have any shape or size suitable for extrusionin a fused filament fabrication process. For example, the build material302 may be in pellet or particulate form for heating and compression, orthe build material 302 may be formed as a wire (e.g., on a spool), abillet, or the like for feeding into an extrusion process. Moregenerally, any geometry that might be suitably employed for heating andextrusion might be used as a form factor for a build material 302 ascontemplated herein. This may include loose bulk shapes such asspherical, ellipsoid, or flaked particles, as well as continuous feedshapes such as a rod, a wire, a filament, a spool, a block or a volumeof pellets.

The build material 302 may include a sinterable build material such as ametal powder loaded into a binder system for heating and extruding usingthe techniques contemplated herein. The binder system renders thecomposition flowable for extrusion and is removed through any of avariety of debinding processes. The powdered material is densified intoa final part through sintering. For example, the build material 302 mayinclude a metal powder formed of aluminum, steel, stainless steel,titanium alloys, and so forth, and the binder system may be formed of awax, a thermoplastic, a polymer, or any other suitable material, as wellas combinations of the foregoing.

Where the build material 302 includes a particulate such as a powderedmaterial for sintering, the particulate can have any size useful forheating and extrusion in a fused filament fabrication process and forsubsequent sintering into a densified object. For example, particles mayhave an average diameter of between about 1 micron and about 100microns, such as between about 5 microns and about 80 microns, betweenabout 10 microns and about 60 microns, between about 15 microns andabout 50 microns, between about 15 microns and about 45 microns, betweenabout 20 microns and about 40 microns, or between about 25 microns andabout 35 microns. For example, in one embodiment, the average diameterof the particulate is between about 25 microns and about 44 microns. Insome embodiments, smaller particles, such as those in the nanometerrange, or larger particle, such as those bigger than 100 microns, canalso or instead be used.

It will be noted that particle sizes are regularly referred to in thisdisclosure. In practice, a single number rarely suffices to accuratelyand fully characterize the shapes, sizes, and size distributions of amixture of particles. For example, a representative diameter may includean arithmetic mean, a volume or surface mean, or a mean diameter overvolume. And relevant rheological properties may depend as much on theparticle shape as the particle size. For non-symmetric distributions,the mean, median and mode may all be different values. Similarly,distribution widths may vary widely, so regardless of the metric that isused, the distribution may be reported as several values such as D10,D50 and D90, which represent the tenth percentile, fiftieth percentile,and ninetieth percentile respectively. In this description, where aspecific metric is provided, then that is the intended metric forcharacterizing a particle size and/or distribution. Otherwise, andparticularly where relative sizes of two or more distributions aregiven, any suitable method may be usefully employed and in general, thesame technique (e.g., measurement instruments and calculations) willpreferably be employed for both values where possible. Unless otherwisespecifically stated, particles should be understood to have any shape orcombination of dimensions, within the stated size range or distribution,suitable for use in the methods, systems, and articles of manufacturecontemplated herein.

In one aspect, metal injection molding compositions may be usefullyadapted for fused filament fabrication systems and other additivefabrication processes. Metal injection molding is a mature technologythat has produced a variety of highly engineered materials with highmetal loading (e.g., >50% by volume, and preferably >60% by volume ormore (where greater metal loading can improve and acceleratessintering)) and good flow properties at elevated temperatures. A varietyof commercially available MIM compositions may be usefully adapted as abuild material for fused filament fabrication. While typical MIMparticles sizes of 50 microns or more are not obviously suited for usewith existing fused filament fabrication (FFF) parts (e.g., nozzles withan exit diameter of 300 microns or less), solid rods of MIM materialwith smaller particle sizes have been demonstrated to extrude well usinga conventional FFF machine with an extrusion diameter of 300 microns anda build material temperature of about 200 degrees Celsius.

In general, the base powder for a build material may be formed of anypowder metallurgy material or other metal or ceramic powder(s) suitablefor sintering. While the particular process, e.g., fused filamentfabrication or stereolithography, may impose dimensional constraints orpreferences on the powdered material, it appears that smaller particlesare generally preferable. Various techniques have been developed formass producing fine metal powders for use in MIM processes. In general,powders may be prepared by crushing, grinding, atomization, chemicalreactions, or electrolytic deposition. Any such powders from five to tenmicrons in size, or from one to twenty microns in size, or from aboutone to fifty microns in size may be used as the powdered base of a buildmaterial as contemplated herein. Smaller particles may also be usedwhere they are available and not prohibitively expensive, and largerparticles may be used provided that they are compatible with printresolution and physical hardware (e.g., an exit nozzle diameter) of afabrication device. While not an absolute limit, particle sizes of atleast one order of magnitude smaller than an exit orifice for anextruder appear to extrude well during FFF-type extrusion processes. Inone embodiment with a 300 μm diameter extrusion, a MIM metal powder withabout 1-22 μm mean diameter may be used, although nano-sized powders canalso or instead be used.

While many suitable powder metallurgy materials are currently available,this type of material—that combines a powdered material for sinteringand a binder for retaining shape net shape and providing a rheologysuitable for FFF extrusion—may be further engineered in a number of waysto facilitate rapid prototyping of sinterable green bodies ascontemplated herein. For example, as noted above a particle size of 100microns or smaller may be usefully employed. In one aspect, theseparticles may be further mixed with smaller nanoparticles (generally ator below one micron in size) of the same material to improve the rate ofsintering.

A wide range of metallic powders may usefully be employed. Powders usingstainless steel, titanium, titanium alloys, high-nickel alloys, nickelcopper alloys, magnetic alloys, and the like are commercially availablein MIM materials and suitable for sintering. Powders of the elementstitanium, vanadium, thorium, niobium, tantalum, calcium, and uraniumhave been produced by high-temperature reduction of the correspondingnitrides and carbides. Iron, nickel, uranium, and berylliumsubmicrometer powders have been demonstrated by reducing metallicoxalates and formates. Exceedingly fine particles also have beenprepared by directing a stream of molten metal through ahigh-temperature plasma jet or flame in order to atomize the material.Various chemical and flame powdering processes may also or instead beused to prevent serious degradation of particle surfaces by atmosphericoxygen. More generally, any technique suitable for producing powderedmetals or other materials suitable for sintering may be adapted for thefabrication of a powdered base material. As a significant advantage,these techniques permit the processing and use of relatively highmelting temperature metals at the significantly lower temperaturesrequired for sintering. Thus, for example, tungsten or steel alloys withmelting temperatures over 1300 degrees Celsius can be usefully sinteredat temperatures below 700 degrees Celsius.

Binders may generally be combined with a powdered build material toprovide a structure matrix that is suitable for deposition (e.g., in afused filament fabrication process), and that will support a fabricatednet shape after initial fabrication through sintering. In contemporaryMIM materials, the binding system may include multiple binders that canbe generally classified as bulk binders and backbone binders (alsoreferred to as primary and secondary binders). The bulk binders can flowat elevated temperatures, and retain the shape of an object after aninitial build in normal atmospheric conditions. The backbone binder willprovide binding later into the sintering process and helps retain theshape as the sintering begins but before substantial sintered strengthhas been achieved. The backbone binder(s) will be the last to gas offduring a sintering process. The binder may vary according to theintended application. For example, the binder may be formed of polymerswith a lower glass transition temperature or less viscosity forhigher-resolution printing.

In general, the binder systems for commercially available MIM materialare not engineered for use in fused fabrication filament processes, andappear to preferably employ polymer mixes that are brittle at roomtemperature. In one aspect, the polymer system of these commerciallyavailable feedstocks may be supplemented with or replaced by a polymerbinder system that is flexible at room temperature so that the buildmaterial can be formed into a filament and wound onto a spool forextended, continuous feeding to a printer. Also, many differentadditives may be included in traditional MIM feedstocks, such aslubricants and release oils, to help injection molded parts through themolding process. However, these may not be desired, and a technique mayinvolve removing them and adding components to the MIM binder that makethe MIM feedstock more printable.

The binder systems described herein may also or instead be adapted foruse with ceramic powders or other materials. The rheology of theextrudate is largely independent of the material that is loaded into thepolymer binder system, and depends more on particle geometry thanparticle composition. As such, any reference to metal injection molding,MIM, or MIM materials should be understood to include ceramics, metaloxides and other powders in a MIM-style binder system, unless adifferent meaning is expressly stated or otherwise clear from thecontext.

Other additives may also or instead be included in an engineeredmaterial as contemplated herein. For example, the material mayincorporate a getter for oxygen or other contaminants as describedabove, particularly when used as a support material. As another example,the material may include a liquid phase or other surface active additiveto accelerate the sintering process.

Any of the foregoing, and similar compositions may be adapted for use asa build material in printing techniques such as fused filamentfabrication. For example, MIM feedstock materials, when suitably shaped,can be extruded through nozzles typical of commercially available FFFmachines, and are generally flowable or extrudable within typicaloperating temperatures (e.g., 160-250 degrees Celsius) of such machines.The working temperature range may depend on the binder—e.g., somebinders achieve appropriate viscosities at about 205 degrees Celsius,while others achieve appropriate viscosities at lower temperatures suchas about 160-180 degrees Celsius. One of ordinary skill will recognizethat these ranges (and all ranges listed herein) are provided by way ofexample and not of limitation.

Any of the foregoing metal injection molding materials, or any othercomposition containing a base of powdered, sinterable material in abinder system may be used as a build material 302 for fused filamentfabrication systems as contemplated herein. Other adaptations of thisbasic composition may be made to render a build material 302 suitablefor stereolithography or other additive fabrication techniques. The termmetal injection molding material, as used herein, is intended to includeany such engineered materials, as well as other fine powder bases suchas ceramics in a similar binder suitable for injection molding. Thus,where the term metal injection molding or the commonly usedabbreviation, MIM, is used herein, this should be understood to includecommercially available metal injection molding materials, as well asother powder and binder systems using powders other than, or in additionto, metals and, thus, should be understood to include ceramics, and allsuch materials are intended to fall within the scope of this disclosureunless a different meaning is explicitly provided or otherwise clearfrom the context. Also, any reference to “MIM materials,” “powdermetallurgy materials,” “MIM feedstocks,” or the like shall generallyrefer to any metal powder and/or ceramic powder mixed with one or morebinding materials or binder systems as contemplated herein, unless adifferent meaning is explicitly provided or otherwise clear from thecontext.

More generally, any powder and binder system forming a sinterable buildmaterial with rheological properties suitable for fused filamentfabrication may be used in an additive fabrication process ascontemplated herein. Such a build material may generally include apowdered material such as a metallic or ceramic powder for forming afinal part and a binder system. The binder system will typically includeone or more binders that retain a net shape of the object 312 duringprocessing into the final part. As discussed above, the processing mayinclude, e.g., debinding the net shape to remove at least a portion ofthe one or more binders and sintering the net shape to join and densifythe powdered material. While powdered metallurgy materials are discussedherein, other powder and binder systems may also or instead be employedin a fused filament fabrication process. Still more generally, it shouldalso be appreciated that other material systems may be suitable forfabricating sinterable net shapes using fabrication techniques such asstereolithography or binderjetting, some of which are discussed ingreater detail below.

A drive system 304 may include any suitable gears, compression pistons,or the like for continuous or indexed feeding of the build material 302into the heating system 306. In another aspect, the drive system 304 mayuse bellows or any other collapsible or telescoping press to drive rods,billets, or similar units of build material into the heating system 306.Similarly, a piezoelectric or linear stepper drive may be used toadvance a unit of build media in an indexed fashion using discretemechanical increments of advancement in a non-continuous sequence ofsteps. For more brittle MIM materials or the like, a fine-toothed drivegear of a material such as a hard resin or plastic may be used to gripthe material without excessive cutting or stress concentrations thatmight otherwise crack, strip, or otherwise compromise the buildmaterial.

The heating system 306 may employ a variety of techniques to heat abuild material to a temperature within a working temperature range wherethe build material 302 has suitable theological properties for extrusionin a fused filament fabrication process. This working temperature rangemay vary according to the type of build material 302, e.g., theconstituent powdered material and binder system, being heated by theheating system 306. Any heating system 306 or combination of heatingsystems suitable for maintaining a corresponding working temperaturerange in the build material 302 where and as needed to drive the buildmaterial 302 to and through the nozzle 310 may be suitably employed as aheating system 306 as contemplated herein.

The robotics 308 may include any robotic components or systems suitablefor moving the nozzles 310 in a three-dimensional path relative to thebuild plate 314 while extruding build material 302 in order to fabricatethe object 312 from the build material 302 according to a computerizedmodel of the object. A variety of robotics systems are known in the artand suitable for use as the robotics 308 contemplated herein. Forexample, the robotics 308 may include a Cartesian coordinate robot orx-y-z robotic system employing a number of linear controls to moveindependently in the x-axis, the y-axis, and the z-axis within the buildchamber 316. Delta robots may also or instead be usefully employed,which can, if properly configured, provide significant advantages interms of speed and stiffness, as well as offering the design convenienceof fixed motors or drive elements. Other configurations such as doubleor triple delta robots can increase range of motion using multiplelinkages. More generally, any robotics suitable for controlledpositioning of a nozzle 310 relative to the build plate 314, especiallywithin a vacuum or similar environment, may be usefully employed,including any mechanism or combination of mechanisms suitable foractuation, manipulation, locomotion, and the like within the buildchamber 316.

The robotics 308 may position the nozzle 310 relative to the build plate314 by controlling movement of one or more of the nozzle 310 and thebuild plate 314. For example, in an aspect, the nozzle 310 is operablycoupled to the robotics 308 such that the robotics 308 position thenozzle 310 while the build plate 314 remains stationary. The build plate314 may also or instead be operably coupled to the robotics 308 suchthat the robotics 308 position the build plate 314 while the nozzleremains stationary. Or some combination of these techniques may beemployed, such as by moving the nozzle 310 up and down for z-axiscontrol, and moving the build plate 314 within the x-y plane to providex-axis and y-axis control. In some such implementations, the robotics308 may translate the build plate 314 along one or more axes, and/or mayrotate the build plate 314. More generally, the robotics 308 may form arobotic system operable to move the one or more nozzles 310 relative tothe build plate 314.

It will be understood that a variety of arrangements and techniques areknown in the art to achieve controlled linear movement along one or moreaxes, and/or controlled rotational motion about one or more axes. Therobotics 308 may, for example, include a number of stepper motors toindependently control a position of the nozzle 310 or build plate 314within the build chamber 316 along each axis, e.g., an x-axis, a y-axis,and a z-axis. More generally, the robotics 308 may include withoutlimitation various combinations of stepper motors, encoded DC motors,gears, belts, pulleys, worm gears, threads, and the like. Any sucharrangement suitable for controllably positioning the nozzle 310 orbuild plate 314 may be adapted for use with the additive manufacturingsystem 300 described herein.

The nozzles 310 may include one or more nozzles for extruding the buildmaterial 302 that has been propelled with the drive system 304 andheated with the heating system 306. While a single nozzle 310 and buildmaterial 302 is illustrated, it will be understood that the nozzles 310may include a number of nozzles that extrude different types of materialso that, for example, a first nozzle 310 extrudes a sinterable buildmaterial while a second nozzle 310 extrudes a support material in orderto support bridges, overhangs, and other structural features of theobject 312 that would otherwise violate design rules for fabricationwith the build material 302. In another aspect, one of the nozzles 310may deposit an interface material for removable or breakaway supportstructures that can be removed after sintering.

In one aspect, the nozzle 310 may include one or more ultrasoundtransducers 330 as described herein. Ultrasound may be usefully appliedfor a variety of purposes in this context. In one aspect, the ultrasoundenergy may facilitate extrusion by mitigating adhesion of a buildmaterial 302 to interior surfaces of the nozzle 310, or improvinglayer-to-layer bonding by encouraging mechanical mixing of materialbetween adjacent layers.

In another aspect, the nozzle 310 may include an inlet gas, e.g., aninert gas, to cool media at the moment it exits the nozzle 310. Moregenerally, the nozzle 310 may include any cooling system for applying acooling fluid to a build material 302 as it exits the nozzle 310. Thisgas jet may, for example, immediately stiffen extruded material tofacilitate extended bridging, larger overhangs, or other structures thatmight otherwise require support structures during fabrication. The inletgas may also or instead carry an abrasive such as dry ice particles forsmoothing surfaces of the object 312.

In another aspect, the nozzle 310 may include one or more mechanisms toflatten a layer of deposited material and apply pressure to bond thelayer to an underlying layer. For example, a heated nip roller, caster,or the like may follow the nozzle 310 in its path through an x-y planeof the build chamber 316 to flatten the deposited (and still pliable)layer. The nozzle 310 may also or instead integrate a forming wall,planar surface, or the like to additionally shape or constrain anextrudate as it is deposited by the nozzle 310. The nozzle 310 mayusefully be coated with a non-stick material (which may vary accordingto the build material 302 being used) in order to facilitate moreconsistent shaping and smoothing by this tool.

In general, the nozzle 310 may include a reservoir, a heater (such asthe heating system 306) configured to maintain a build material 302within the reservoir in a liquid or otherwise extrudable form, and anoutlet. Where the printer 301 includes multiple nozzles 310, a secondnozzle may usefully provide any of a variety of additional buildmaterials, support materials, interface materials, and so forth.

For example, the second nozzle 310 may supply a support material withdebind and sintering shrinkage properties suitable for maintainingsupport of an object during processing into a final part. For example,this may include a material consisting of, e.g., the binder system forthe sinterable build material without the powdered material that sintersinto the final object. In another aspect, the support material may beformed of a wax, or some other thermoplastic or other polymer that canbe removed during processing of a printed green body. This supportmaterial may, for example, be used for overhang supports, as well as fortop or side supports, or any other suitable support structures toprovide a physical support during printing and subsequent sintering. Itwill be understood that printing and sintering may impose differentsupport requirements. As such, different support materials and ordifferent support rules may be employed for each type of requiredsupport. Additionally, where a print support is not required duringsintering, the print support may be removed after a print and beforesintering, while sintering supports would be left attached to the greenobject until sintering is completed (or until the object achieves asufficient sinter strength to eliminate the need for the sinteringsupport structures).

In another aspect, the second nozzle (or a third nozzle) may be used toprovide an interface material. In one aspect, e.g., where the supportmaterial is a ceramic/binder system that debinds and sinters into anunstructured powder, the support material may also usefully serve as theinterface material and form an interface layer that does not sintertogether with the build material 302 of the object. In another aspect,the second nozzle (or a third nozzle) may provide an interface materialthat is different from the support material. This may, for example,include the binder system of the build material 302 (or supportmaterial), along with a ceramic or some other material that will notsinter under the time and temperature conditions used to sinter thepowdered material in the build material 302 that forms the object 312.This may also or instead include a material that forms a brittleinterface with the sintered part so that it can break away from thefinal object easily after sintering. Where this interface material doesnot sinter, it may be used in combination with a sinterable supportstructure that can continue to provide structural support during asintering process.

The support material(s) may usefully integrate other functionalsubstances. For example, titanium may be added to the support materialas an oxygen getter to improve the build environment without introducingany titanium into the fabricated object. More generally, the supportmaterial (or an interface material of a layer between the supportmaterial and the object 312) may include a constituent with asubstantially greater chemical affinity for oxygen than the buildmaterial 302, in order to mitigate oxidation of the build material 302during fabrication. Other types of additives may also or instead be usedto remove contaminants. For example, a zirconium powder (or other strongcarbide former) may be added to the support material in order to extractcarbon contamination during sintering.

The object 312 may be any object suitable for fabrication using thetechniques contemplated herein. This may include functional objects suchas machine parts, aesthetic objects such as sculptures, or any othertype of objects, as well as combinations of objects that can be fitwithin the physical constraints of the build chamber 316 and build plate314. Some structures such as large bridges and overhangs cannot befabricated directly using FFF because there is no underlying physicalsurface onto which a material can be deposited. In these instances, asupport structure 313 may be fabricated, preferably of a soluble orotherwise readily removable material, in order to support acorresponding feature of the object 312. An interface layer may also befabricated or otherwise formed between the support structure 313 and theobject 312 to facilitate separation of the two structures aftersintering or other processing.

The build plate 314 may be formed of any surface or substance suitablefor receiving deposited metal or other materials from the nozzles 310.The surface of the build plate 314 may be rigid and substantiallyplanar. In one aspect, the build plate 314 may be heated, e.g.,resistively or inductively, to control a temperature of the buildchamber 316 or a surface upon which the object 312 is being fabricated.This may, for example, improve adhesion, prevent thermally induceddeformation or failure, and facilitate relaxation of stresses within theobject 312. In another aspect, the build plate 314 may be a deformablestructure or surface that can bend or otherwise physically deform inorder to detach from a rigid object 312 formed thereon. The build plate314 may be movable within the build chamber 316, e.g., by a positioningassembly (e.g., the same robotics 308 that position the nozzle 310 ordifferent robotics). For example, the build plate 314 may be movablealong a z-axis (e.g., up and down-toward and away from the nozzle 310),or along an x-y plane (e.g., side to side, for instance in a patternthat forms the tool path or that works in conjunction with movement ofthe nozzle 310 to form the tool path for fabricating the object 312), orsome combination of these. In an aspect, the build plate 314 isrotatable.

The build plate 314 may include a temperature control system formaintaining or adjusting a temperature of at least a portion of thebuild plate 314. The temperature control system may be wholly orpartially embedded within the build plate 314. The temperature controlsystem may include without limitation one or more of a heater, coolant,a fan, a blower, or the like. In implementations, temperature may becontrolled by induction heating of the metallic printed part. The buildplate 314 may usefully incorporate a thermal control system 317 forcontrollably heating and/or cooling the build plate 314 during aprinting process.

In general, the build chamber 316 houses the build plate 314 and thenozzle 310, and maintains a build environment suitable for fabricatingthe object 312 on the build plate 314 from the build material 302. Whereappropriate for the build material 302, this may include a vacuumenvironment, an oxygen depleted environment, a heated environment, aninert gas environment, and so forth. The build chamber 316 may be anychamber suitable for containing the build plate 314, an object 312, andany other components of the printer 301 used within the build chamber316 to fabricate the object 312.

The printer 301 may include a pump 324 coupled to the build chamber 316and operable to create a vacuum within the build chamber 316 orotherwise filter or handle air during a printing process. While powderedmetallurgy materials and other powder/binder systems contemplated hereinwill not typically require a vacuum environment, a vacuum maynonetheless be used to reduce contaminants or otherwise control theoperating environment for a printing process. A number of suitablevacuum pumps are known in the art and may be adapted for use as the pump324 contemplated herein. The build chamber 316 may form anenvironmentally sealed chamber so that it can be evacuated with the pump324, or so that temperature and air flow through the build chamber 316can be controlled. The environmental sealing may include thermalsealing, e.g., to prevent an excess of heat transfer from heatedcomponents within the build volume to an external environment, andvice-versa. The seal of the build chamber 316 may also or insteadinclude a pressure seal to facilitate pressurization of the buildchamber 316, e.g., to provide a positive pressure that resistsinfiltration by surrounding oxygen and other ambient gases or the like.To maintain the seal of the build chamber 316, any openings in anenclosure of the build chamber 316, e.g., for build material feeds,electronics, and so on, may include suitably corresponding vacuum sealsor the like.

The build chamber 316 may include a temperature control system 328 formaintaining or adjusting a temperature of at least a portion of a volumeof the build chamber 316 (e.g., the build volume). The temperaturecontrol system 328 may include without limitation one or more of aheater, a coolant, a fan, a blower, or the like. The temperature controlsystem 328 may use a fluid or the like as a heat exchange medium fortransferring heat as desired within the build chamber 316. Thetemperature control system 328 may also or instead move air (e.g.,circulate air) within the build chamber 316 to control temperature, toprovide a more uniform temperature, or to transfer heat within the buildchamber 316.

The temperature control system 328, or any of the temperature controlsystems described herein (e.g., a temperature control system of theheating system 306 or a temperature control system of the build plate314) may include one or more active devices such as resistive elementsthat convert electrical current into heat, Peltier effect devices thatheat or cool in response to an applied current, or any otherthermoelectric heating and/or cooling devices. Thus, the temperaturecontrol systems discussed herein may include a heater that providesactive heating to the components of the printer 301, a cooling elementthat provides active cooling to the components of the printer 301, or acombination of these. The temperature control systems may be coupled ina communicating relationship with the control system 318 in order forthe control system 318 to controllably impart heat to or remove heatfrom the components of the printer 301. It will be further understoodthat the temperature control system 328 for the build chamber 316, thetemperature control system of the heating system 306, and thetemperature control system of the build plate 314, may be included in asingular temperature control system (e.g., included as part of thecontrol system 318 or otherwise in communication with the control system318) or they may be separate and independent temperature controlsystems. Thus, for example, a heated build plate or a heated nozzle maycontribute to heating of the build chamber 316 and form a component of atemperature control system 328 for the build chamber 316.

In general, a control system 318 may include a controller or the likeconfigured by computer executable code to control operation of theprinter 301. The control system 318 may be operable to control thecomponents of the additive manufacturing system 300, such as the nozzle310, the build plate 314, the robotics 308, the various temperature andpressure control systems, and any other components of the additivemanufacturing system 300 described herein to fabricate the object 312from the build material 302 based on a three-dimensional model 322 orany other computerized model describing the object 312. The controlsystem 318 may include any combination of software and/or processingcircuitry suitable for controlling the various components of theadditive manufacturing system 300 described herein including withoutlimitation microprocessors, microcontrollers, application-specificintegrated circuits, programmable gate arrays, and any other digitaland/or analog components, as well as combinations of the foregoing,along with inputs and outputs for transceiving control signals, drivesignals, power signals, sensor signals, and the like. In one aspect, thecontrol system 318 may include a microprocessor or other processingcircuitry with sufficient computational power to provide relatedfunctions such as executing an operating system, providing a graphicaluser interface (e.g., to a display coupled to the control system 318 orprinter 301), converting three-dimensional models 322 into toolinstructions, and operating a web server or otherwise hosting remoteusers and/or activity through a network interface 362 for communicationthrough a network 360.

The control system 318 may include a processor and memory, as well asany other co-processors, signal processors, inputs and outputs,digital-to-analog or analog-to-digital converters, and other processingcircuitry useful for controlling and/or monitoring a fabrication processexecuting on the printer 301, e.g., by providing instructions to controloperation of the printer 301. To this end, the control system 318 may becoupled in a communicating relationship with a supply of the buildmaterial 302, the drive system 304, the heating system 306, the nozzles310, the build plate 314, the robotics 308, and any otherinstrumentation or control components associated with the build processsuch as temperature sensors, pressure sensors, oxygen sensors, vacuumpumps, and so forth.

The control system 318 may generate machine-ready code for execution bythe printer 301 to fabricate the object 312 from the three-dimensionalmodel 322. In another aspect, the machine-ready code may be generated byan independent computing device 364 based on the three-dimensional model322 and communicated to the control system 318 through a network 360,which may include a local area network or an internetwork such as theInternet, and the control system 318 may interpret the machine-readycode and generate corresponding control signals to components of theprinter 301. The control system 318 may deploy a number of strategies toimprove the resulting physical object structurally or aesthetically. Forexample, the control system 318 may use plowing, ironing, planing, orsimilar techniques where the nozzle 310 is run over existing layers ofdeposited material, e.g., to level the material, remove passivationlayers, or otherwise prepare the current layer for a next layer ofmaterial and/or shape and trim the material into a final form. Thenozzle 310 may include a non-stick surface to facilitate this plowingprocess, and the nozzle 310 may be heated and/or vibrated (using theultrasound transducer) to improve the smoothing effect. In one aspect,these surface preparation steps may be incorporated into theinitially-generated machine ready code such as g-code derived from athree-dimensional model and used to operate the printer 301 duringfabrication. In another aspect, the printer 301 may dynamically monitordeposited layers and determine, on a layer-by-layer basis, whetheradditional surface preparation is necessary or helpful for successfulcompletion of the object 312. Thus, in one aspect, there is disclosedherein a printer 301 that monitors a metal FFF process and deploys asurface preparation step with a heated or vibrating non-stick nozzlewhen a prior layer of the metal material is unsuitable for receivingadditional metal material.

In general, a three-dimensional model 322 or other computerized model ofthe object 312 may be stored in a database 320 such as a local memory ofa computing device used as the control system 318, or a remote databaseaccessible through a server or other remote resource, or in any othercomputer-readable medium accessible to the control system 318. Thecontrol system 318 may retrieve a particular three-dimensional model 322in response to user input, and generate machine-ready instructions forexecution by the printer 301 to fabricate the corresponding object 312.This may include the creation of intermediate models, such as where aCAD model is converted into an STL model, or other polygonal mesh orother intermediate representation, which can in turn be processed togenerate machine instructions such as g-code for fabrication of theobject 312 by the printer 301.

In operation, to prepare for the additive manufacturing of an object312, a design for the object 312 may first be provided to a computingdevice 364. The design may be a three-dimensional model 322 included ina CAD file or the like. The computing device 364 may in general includeany devices operated autonomously or by users to manage, monitor,communicate with, or otherwise interact with other components in theadditive manufacturing system 300. This may include desktop computers,laptop computers, network computers, tablets, smart phones, smartwatches, or any other computing device that can participate in thesystem as contemplated herein. In one aspect, the computing device 364is integral with the printer 301.

The computing device 364 may include the control system 318 as describedherein or a component of the control system 318. The computing device364 may also or instead supplement or be provided in lieu of the controlsystem 318. Thus, unless explicitly stated to the contrary or otherwiseclear from the context, any of the functions of the computing device 364may be performed by the control system 318 and vice-versa. In anotheraspect, the computing device 364 is in communication with or otherwisecoupled to the control system 318, e.g., through a network 360, whichmay be a local area network that locally couples the computing device364 to the control system 318 of the printer 301, or an internetworksuch as the Internet that remotely couples the computing device 364 in acommunicating relationship with the control system 318.

The computing device 364 (and the control system 318) may include aprocessor 366 and a memory 368 to perform the functions and processingtasks related to management of the additive manufacturing system 300 asdescribed herein. In general, the memory 368 may contain computer codethat can be executed by the processor 366 to perform the various stepsdescribed herein, and the memory may further store data such as sensordata and the like generated by other components of the additivemanufacturing system 300.

In general, a fabrication process such as fused filament fabricationimplies, or expressly includes, a set of design rules to accommodatephysical limitations of a fabrication device and a build material. Forexample, an overhang cannot be fabricated without positioning a supportstructure underneath. While the design rules for a process such as fusedfilament fabrication (FFF) will apply to fabrication of a green bodyusing FFF techniques as described herein, the green body will also besubject to various debinding and sintering rules. This may, for example,include a structure to prevent or minimize drag on a floor while a partshrinks during sintering (which may be 20% or more depending on thecomposition of the green body). Similarly, certain supports are requiredduring sintering that are different than the supports required duringfused filament fabrication. Where parts are nested, such as a pair ofoverlapping cantilevered beams, it may also be important for interveningsupport structures to shrink slightly more quickly than the supportedstructures in order to prevent capturing and potentially deforming thecantilevers. As another example, injection molding typically aims foruniform wall thickness to reduce variability in debinding and/orsintering behaviors, with thinner walls being preferred. The systemcontemplated herein will apply these disparate sets of designrules-those for the rapid prototyping system (e.g., fused filamentfabrication), those for debinding, and those for sintering process—to aCAD model that is being prepared for fabrication so that an object maybe fabricated from the CAD model and further processed whilesubstantially retaining a desired or intended net shape.

These rules may also be combined under certain conditions. For example,the support structures required for an overhang during fabrication mustresist the force of an extrusion/deposition process used to fabricate abottom surface of the overhang, whereas the support structure duringsintering only needs to resist the forces of gravity during the bakingprocess. Thus, there may be two separate supports that are removed atdifferent times during a fabrication process: the fabrication supportsthat are configured to resist the force of a fabrication process whichmay be configured to breakaway from a loose mechanical coupling to agreen body, and sintering supports that may be less extensive, and onlyneed to resist the gravitation forces on a body during sintering. Theselatter supports are preferably coupled to the object through anon-sinterable layer to permit easy removal from the densified finalobject. In another aspect, the fabrication supports may be fabricatedfrom binder without a powder or other fill so that they completelydisappear during a sintering process.

During fabrication, detailed data may be gathered for subsequent use andanalysis. This may, for example, include data from a sensor and computervision system that identifies errors, variations, or the like that occurin each layer of an object 312. Similarly, tomography or the like may beused to detect and measure layer-to-layer interfaces, aggregate partdimensions, and so forth. This data may be gathered and delivered withthe object to an end user as a digital twin 340 of the object 312, e.g.,so that the end user can evaluate how variations and defects mightaffect use of the object 312. In addition to spatial/geometric analysis,the digital twin 340 may log process parameters including, e.g.,aggregate statistics such as weight of material used, time of print,variance of build chamber temperature, and so forth, as well aschronological logs of any process parameters of interest such asvolumetric deposition rate, material temperature, environmenttemperature, and so forth.

The digital twin 340 may also usefully log a thermal history of thebuild material 302, e.g., on a voxel-by-voxel or other volumetric basiswithin the completed object 312. Thus, in one aspect, the digital twin340 may store a spatial temporal map of thermal history for buildmaterial that is incorporated into the object 312, which may be used,e.g., to estimate an onset of early sintering, loss of binder system, orother possible thermal effects that might accumulate during afabrication process. The control system 318 may use this informationduring fabrication, and may be configured to adjust a thermal parameterof a fused filament fabrication system or the like during fabricationaccording to the spatial temporal map of thermal history. For example,the control system 318 may usefully cool a build chamber or control anextrusion temperature to maintain a more uniform degree of thermaldebind throughout the fabricated object 312.

The printer 301 may include a camera 350 or other optical device. In oneaspect, the camera 350 may be used to create the digital twin 340 orprovide spatial data for the digital twin 340. The camera 350 may moregenerally facilitate machine vision functions or facilitate remotemonitoring of a fabrication process. Video or still images from thecamera 350 may also or instead be used to dynamically correct a printprocess, or to visualize where and how automated or manual adjustmentsshould be made, e.g., where an actual printer output is deviating froman expected output. The camera 350 can be used to verify a position ofthe nozzle 310 and/or build plate 314 prior to operation. In general,the camera 350 may be positioned within the build chamber 316, orpositioned external to the build chamber 316, e.g., where the camera 350is aligned with a viewing window formed within a chamber wall.

The additive manufacturing system 300 may include one or more sensors370. The sensor 370 may communicate with the control system 318, e.g.,through a wired or wireless connection (e.g., through a data network360). The sensor 370 may be configured to detect progress of fabricationof the object 312, and to send a signal to the control system 318 wherethe signal includes data characterizing progress of fabrication of theobject 312. The control system 318 may be configured to receive thesignal, and to adjust at least one parameter of the additivemanufacturing system 300 in response to the detected progress offabrication of the object 312. The one or more sensors 370 may includewithout limitation one or more of a contact profilometer, a non-contactprofilometer, an optical sensor, a laser, a temperature sensor, motionsensors, an imaging device, a camera, an encoder, an infrared detector,a volume flow rate sensor, a weight sensor, a sound sensor, a lightsensor, a sensor to detect a presence (or absence) of an object, and soon.

As discussed herein, the control system 318 may adjust a parameter ofthe additive manufacturing system 300 in response to the sensor 370. Theadjusted parameter may include a temperature of the build material 302,a temperature of the build chamber 316 (or a portion of a volume of thebuild chamber 316), and a temperature of the build plate 314. Theparameter may also or instead include a pressure such as an atmosphericpressure within the build chamber 316. The parameter may also or insteadinclude an amount or concentration of an additive for mixing with thebuild material such as a strengthening additive, a colorant, anembrittlement material, and so forth.

The nozzle 310 may be configured to transmit a signal to the controlsystem 318 indicative of any sensed condition or state such as aconductivity of the build material 302, a type of the build material302, a diameter of an outlet of the nozzle 310, a force exerted by thedrive system 304 to extrude build material 302, a temperature of theheating system 306, or any other useful information. The control system318 may receive any such signal and control an aspect of the buildprocess in response.

In one aspect, the one or more sensors 370 may include a sensor systemconfigured to volumetrically monitor a temperature of a build material302, that is, to capture temperature at specific locations within avolume of the build material 302 before extrusion, during extrusion,after extrusion, or some combination of these. This may include surfacemeasurements where available, based on any contact or non-contacttemperature measurement technique. This may also or instead include anestimation of the temperature within an interior of the build material302 at different points along the feed path and within the completedobject. Using this accumulated information, a thermal history may becreated that includes the temperature over time for each voxel of buildmaterial within the completed object 312, all of which may be stored inthe digital twin 340 described below and used for in-process control ofthermal parameters during printing, control of downstream processingsuch as debinding and sintering, or post-process review and analysis ofthe object 312.

The additive manufacturing system 300 may include, or be connected in acommunicating relationship with, a network interface 362. The networkinterface 362 may include any combination of hardware and softwaresuitable for coupling the control system 318 and other components of theadditive manufacturing system 300 in a communicating relationship to aremote computer (e.g., the computing device 364) through a data network360. By way of example and not limitation, this may include electronicsfor a wired or wireless Ethernet connection operating according to theIEEE 802.11 standard (or any variation thereof), or any other short orlong range wireless networking components or the like. This may includehardware for short range data communications such as Bluetooth or aninfrared transceiver, which may be used to couple to a local areanetwork or the like that is in turn coupled to a wide area data networksuch as the Internet. This may also or instead include hardware/softwarefor a WiMAX connection or a cellular network connection (using, e.g.,CDMA, GSM, LTE, or any other suitable protocol or combination ofprotocols). Consistently, the control system 318 may be configured tocontrol participation by the additive manufacturing system 300 in anynetwork 360 to which the network interface 362 is connected, such as byautonomously connecting to the network 360 to retrieve printablecontent, or responding to a remote request for status or availability ofthe printer 301.

Other useful features may be integrated into the printer 301 describedabove. For example, the printer 301 may include a solvent source andapplicator, and the solvent (or other material) may be applied to aspecific (e.g., controlled by the printer 301) surface of the object 312during fabrication, such as to modify surface properties. The addedmaterial may, for example, intentionally oxidize or otherwise modify asurface of the object 312 at a particular location or over a particulararea in order to provide a desired electrical, thermal, optical,mechanical, or aesthetic property. This capability may be used toprovide aesthetic features such as text or graphics, or to providefunctional features such as a window for admitting RF signals. This mayalso be used to apply a release layer or modify an existing support orobject layer for breakaway support.

In some implementations, the computing device 364 or the control system318 may identify or create a support structure 313 that supports aportion of the object 312 during fabrication. In general, the supportstructure 313 may be a sacrificial structure that is removed afterfabrication has been completed. In some such implementations, thecomputing device 364 may identify a technique for manufacturing thesupport structure 313 based on factors such as the object 312 beingmanufactured, the materials being used to manufacture the object 312,and user input. The support structure 313 may be fabricated from ahigh-temperature polymer or other material that will form a weak bond tothe build material 302. In another aspect, an interface between thesupport structure 313 and the object 312 may be manipulated to weakenthe interlayer bond to facilitate the fabrication of breakaway support.

The printer 301 may also usefully integrate a supplemental tool 380 suchas a subtractive fabrication tool (e.g., a drill, a milling tool, orother multi-axis controllable tool) for removing material from theobject 312 that deviates from an expected physical output based on thethree-dimensional model 322 used to fabricate the object 312. A millingtool, for example, may be configured for shaping the build material onthe build plate 314 after extrusion from the extruder 390 and prior tosintering of the object 314. While combinations of additive andsubtractive technologies have been contemplated, the use of MIMmaterials provides a unique advantage when subtractive shaping isperformed on a green object after net shape forming but before sintering(or debinding), where the object 112 is relatively soft and workable.This permits quick and easy removal of physically observable defects andprinting artifacts before the object 112 is sintered into a metalobject. This may also include imposing certain features or structuresonto the object, either according to the three-dimensional model 322 orsome other manual specification or the like. For example, this mayinclude tapping threads into the object, or creating through holes orother structures that can be readily imposed by a subtractive drilling,grinding, routing, or other subtractive process. This approach may beparticularly advantageous where the feature of interest, e.g., ahorizontal threaded through-hole, might be more difficult to accuratelyfabricate with additive manufacturing. Where subtractive fabrication isspecified within the part, the additive model may also include adequatelayer thicknesses and infill, e.g., in a fused filament fabricationprocess, to provide adequate material clearances around the subtractedfeature.

In another aspect, the supplemental tool 380 may be a tool forfabricating overhead supports as described herein. For example, thesupplemental tool 380 may include a supplemental additive fabricationsystem configured to form a support structure above a surface of anobject, the surface being upwardly vertically exposed and the supportstructure including a superstructure coupled to the surface to support adownward vertical load on the object. Suitable overhead supportstructures are described by way of example with reference to FIGS. 9-10below.

In one general aspect, the drive system 304, the heating system 306, thenozzle 310 and any other complementary components may form an extruder390 for extruding one of the materials described herein, and the printer300 may include any number of such extruders 390 according to the numberand type of materials used in a fabrication process. Thus, there isgenerally disclosed herein a printer 300 for three-dimensionalfabrication, the printer 400 including a build plate 314, a firstextruder 390, a second extruder 390, a robotic system including robotics308 operable to move the first extruder 390 and the second extruder 390relative to the build plate 314, and a processor (e.g., the processor ofthe control system 318). The first extruder 390 may be coupled to afirst source of a build material 302 for fabricating an object 312,where the build material 302 includes a powdered material for formingthe object 312 and a binder system including one or more binders, wherethe one or more binders resist deformation of a net shape of the object312 during processing of the object into a final part. The secondextruder 390 may be coupled to a second source of an interface materialfor fabricating an interface layer between the object 312 and anadjacent surface of a support structure 313, where the interfacematerial resists bonding of the object 312 to the support structure 313during sintering. The processor may be configured by computer executablecode to move the robotic system along a build path relative to the buildplate 314 while extruding from at least one of the first extruder 390and the second extruder 390 to fabricate the object 312 on the buildplate 314 based on a computerized model (e.g., the three-dimensionalmodel 322) of the object 314.

The first extruder 390 may be the second extruder 390, e.g., where theprinter 300 uses material swapping to switch between a build materialand an interface material for the single extruder. The printer 300 mayalso or instead include a third extruder 390 coupled to a third sourceof a support material for fabricating the support structure 313, or to asecond build material for use in multi-material fabrication. In anotheraspect, the support structure 313 may be formed of the same material asthe object 312, e.g., where the processor is configured to form thesupport structure 313 by extruding the build material 302 from the firstextruder 390.

FIG. 4 shows an additive manufacturing system using binder jetting. Ascontemplated herein, binder jetting techniques can be used to depositand bind metallic particles or the like in a net shape for debinding andsintering into a final part. Where support structures are required tomitigate deformation of the object during the debinding and/orsintering, an interface layer may be formed between the supportstructures and portions of the object in order to avoid bonding of thesupport structure to the object during sintering.

In general, a printer 400 for binder jetting may include a powder bed402, a spreader 404 (e.g., a roller) movable across the powder bed 402,a print head 406 movable across the powder bed 402, and a controller 408in electrical communication with the print head 406. The powder bed 402can include, for example, a packed quantity of a powder 410 ofmicroparticles of a first metal. The spreader 404 can be movable acrossthe powder bed 402 to spread a layer of powder 410 from a supply 412 ofa powdered material across the powder bed 402. In one aspect, thespreader 404 may be a bi-directional spreader configured to spreadpowder from the supply 412 in one direction, and from a second supply(not shown) on an opposing side of the powder bed 402 in a returndirection in order to speed the processing time for individual layers.

The print head 406 can define a discharge orifice and, in certainimplementations, can be actuated (e.g., through delivery of an electriccurrent to a piezoelectric element in mechanical communication with thebinder 414) to dispense a binder 414 through the discharge orifice tothe layer of powder spread across the powder bed 402. The binder 414 caninclude a carrier and nanoparticles of a second metal dispersed in thecarrier and, when dispersed onto the powder layer, can fill asubstantial portion of void space of the powder 410 in the layer suchthat the nanoparticles of the binder 414 are dispersed among thenanoparticles of the powder 410 in the layer. The nanoparticles of thebinder 414 can have a lower sinter temperature than the microparticlesof the powder 410, and the distribution of nanoparticles throughout themicroparticles in the powder bed 402 can facilitate formation of sinternecks in situ in a three-dimensional object 416 in the powder bed 402.As compared to a three-dimensional object without such sinter necks, thethree-dimensional object 416 with sinter necks can have greater strengthand, therefore, be less prone to sagging or other deformation as thethree-dimensional object 416 is subject to subsequent processing to forma final part.

The supply 412 of the powdered material may provide any materialsuitable for use as a build material as contemplated herein, such as asinterable powder of material selected for a final part to be formedfrom the object 416. The supply 412 and the spreader 404 may supply thepowdered material to the powder bed 402, e.g., by lifting the powder 410and displacing the powder to the powder bed 402 using the spreader 404,which may also spread the powdered material across the powder bed 402 ina substantially uniform layer for binding with the print head 406.

In use, the controller 408 can actuate the print head 406 to deliver thebinder 414 from the print head 406 to each layer of the powder 410 in acontrolled two-dimensional pattern as the print head 406 moves acrossthe powder bed 402. It should be appreciated that the movement of theprint head 406 and the actuation of the print head 406 to deliver thebinder 414 can be done in coordination with movement of the spreader 404across the print bed. For example, the spreader 404 can spread a layerof the powder 410 across the print bed, and the print head 406 candeliver the binder 414 in a controlled two-dimensional pattern to thelayer of the powder 410 spread across the print bed to form a layer of athree-dimensional object 416. These steps can be repeated (e.g., withcontrolled two-dimensional pattern for each respective layer) insequence to form subsequent layers until, ultimately, thethree-dimensional object 416 is formed in the powder bed 402. Thus, theprinter 400 may be configured to apply a binder 414 to a top surface 415of the powdered material (e.g., the powder 410) in the powder bed 402according to a computerized model of the object 416. The printer 400 maymore specifically be configured to apply the binder 414 according to atwo-dimensional cross section of the computerized model and to apply asecond binder (which may be the binder 414 for the object) in a secondpattern to bind other regions of the powdered material to form a supportstructure 420 adjacent to at least one surface of the object 416. Thismay, for example, be based on a second computerized model of a sintersupport for the object, e.g., to support various features of the object416 against collapse or other deformation during sintering. Where aninterface layer 422 is used, the binder and the second binder may be asubstantially similar or identical binder system deposited from a singleprint head.

In certain implementations, the additive manufacturing system canfurther include a heater 418 in thermal communication with the powderbed 402. For example, the heater 418 can be in conductive thermalcommunication with the powder bed 402. As a specific example, the heater418 can be a resistance heater embedded in one or more walls defining avolume of the powder bed 402. Additionally, or alternatively, the heater418 can be an induction heater.

The heater 418 can be controlled (e.g., through electrical communicationwith the controller 408) to heat the three-dimensional object 416 in thepowder bed 402 to a target temperature (e.g., greater than about 100degrees Celsius and less than about 600 degrees Celsius). For example,in instances in which the nanoparticles sinter at a lower temperaturethan the microparticles, the target temperature can be greater than asintering temperature of the nanoparticles and less than a sinteringtemperature of the microparticles. It should be appreciated that, atsuch a target temperature, the nanoparticles of the binder 414 cansinter while the microparticles remain relatively unsintered. Becausethe nanoparticles are selectively distributed in the powder bed 402,through the controlled two-dimensional pattern of the binder 414 in eachlayer of the three-dimensional object 416, such preferential sinteringof the nanoparticles in the powder bed 402 can produce sinter necksthroughout the three-dimensional object 416. In general, the presence ofthese sinter necks throughout the three-dimensional object 416strengthens the three-dimensional object 416. The strengthenedthree-dimensional object 416 can be removed from the powder bed 402 andsubjected to one or more finishing process with a reduced likelihood ofdeformation or other defects, as compared to a three-dimensional objectwithout sinter necks.

While the technique described above may facilitate improved sinteringproperties in a green part or other pre-sintered net shape object,structural support may nonetheless be required. In such instances, asupport structure 420 may be fabricated under the three-dimensionalobject 416 to provide support against drooping or other deformationduring sintering. In these instances, a deposition tool 460 may beconfigured to apply an interface material at an interface between thesupport structure 420 and the object 416 that resists bonding of thesupport structure 420 to the object 416 during sintering at sinteringtemperatures suitable for the powder 410. Thus, the deposition tool 460may be used to form an interface layer 422 between the support structure420 and the object 416, e.g., by inhibiting or preventing sintering ofpowder 410 from the powder bed 402 that remains between the supportstructure 420 and the object 416 when sintering begins. In general, thedeposition tool 460 may be a jetting print head or any other tool orcombination of tools suitable for depositing a corresponding layer ofmaterial in a controlled pattern to form the interface layer 422. Thedeposition tool 460 may, for example, deposit a colloidal suspension ofsmall (relative to the powder 410) nano-particles of a high-temperaturesintering material (also relative to the powder 410). For example, thepowder 410 may be a metallic powder such as a sinterable metal powderwith a mean particle size of at least fifteen microns, or mean particlesize of about ten to thirty-five microns, and the deposition tool 460may deposit a colloidal suspension of ceramic particles sized toinfiltrate the sinterable powder in a surface of the support structure420 adjacent to the object 416. The ceramic particles may, for example,have a mean particle size of one micron or less, or at least one orderof magnitude smaller than a similarly measured mean particle size of thesinterable powder. These smaller particles may infiltrate the powder 410in the interface layer 422 and form a barrier to formation of necksbetween the particles of the powder 410.

In another aspect, the interface material may include a layer of ceramicparticles deposited at a surface of the support structure 420 adjacentto the object 416. These ceramic particles may be solidified, e.g., in abinder or the like to prevent displacement by subsequent layers of thesinterable powder, thus forming a sinter-resistant ceramic layer betweenthe support structure 420 and the object 416. The ceramic particles may,for example, be deposited in a carrier that gels upon contact with thesinterable powder in the powder bed 402, or in a curable carrier, wherea curing system such as a light source or heat source is configured tocure the curable carrier substantially concurrently with deposition onthe sinterable powder, e.g., to prevent undesired infiltration into anyadjacent regions of the support structure 420 or the object 416. Inanother aspect, the interface material may include a material thatremains as an interface layer physically separating the supportstructure from the object after debind and into a thermal sinteringcycle, e.g., where a ceramic powder layer is deposited and cured intoposition before another layer of powder 410 is spread over the powderbed 402. In one aspect, the interface material may be deposited in anintermittent pattern such as an array of non-touching hexagons betweenthe support structure 420 and the object 416 to create a correspondingpattern of gaps between the support structure and the object aftersintering. This latter structure may usefully weaken a mechanicalcoupling between the support structure 420 and the object 416 tofacilitate removal of the support structure 420 after sintering.

Other suitable techniques for forming a sinter-resistant layer on asinterable three-dimensional object are described by way of non-limitingexamples, in Khoshnevis, et al., “Metallic part fabrication usingselective inhibition sintering (SIS),” Rapid Prototyping Journal, Vol.18:2, pp. 144-153 (2012) and U.S. Pat. No. 7,291,242 to Khoshnevis, eachof which is hereby incorporated by reference in its entirety. By way ofnon-limiting example, suitable techniques for inhibiting sintering on asurface of an object include the use of a ceramic as a macroscopicmechanical inhibitor, an application of lithium chloride and aluminumsulfate as microscopic mechanical inhibitors, and an application ofsulfuric acid and hydrogen peroxide as chemical inhibitors. Moregenerally, any technique for mechanically, chemically or otherwiseinhibiting sintering may be usefully employed to create an interfacelayer 422 within the powder bed 410 to facilitate post-sinteringseparation of the object 416 and the support structure 420.

A variety of useful material systems may be adapted for use in a printer400 that uses binder jetting to fabricate an interface layer between asupport structure and an object. For example, the interface material mayusefully contain a soluble metal salt that transforms to a ceramic upondehydration and heating, such as a salt containing at least one of ahydroxide, a chloride, a sulfate, a nitrate, an acetate, and a stearate.The interface material may also or instead include an aluminum, and theinterface material may include at least one of zirconium, yttrium,silicon, titanium, iron, magnesium, and calcium. In another aspect, thebinder may include a secondary infiltrant selected to modify propertiesof the final part, such as at least one of a carbon, a boron, and ametal salt.

FIG. 5 shows a stereolithography system. The stereolithography system500 can be used to form a three-dimensional object 502 from a resin 504by selectively exposing the resin 504 to activation energy from anactivation light source 506. The resin 504 can include particlessuspended in a plurality of binders, which can include a first binderand a second binder different from the first binder and in a mixturewith the first binder. For example, the first binder can besubstantially non-reactive under exposure to wavelengths of lightsufficient to crosslink or polymerize the second binder such that thesecond binder can undergo crosslinking and/or polymerization locallywithin the stereolithography system 500 to form a layer of an objectand, through layer-by-layer exposure of the second binder to activationlight, ultimately form a green part, such as the three-dimensionalobject 502. As also described in greater detail below, the first bindercan have sufficient strength to support a green part formed from theresin 504 and, additionally or alternatively, can be extractable (e.g.,through a first debinding process) from the three-dimensional object 502to leave behind the crosslinked and/or polymerized second binder and themetal particles suspended in the second binder. The second binder, asfurther described below, can be removed from the particles though asecond debinding process, and the particles can undergo subsequentprocessing (e.g., sintering) to form a finished part from thethree-dimensional object 502. Additionally, or alternatively, the secondbinder can be removed from the first binder and/or from the particlesthrough the second debinding process. Thus, more generally, the firstdebinding processes and the second debinding processes described hereinshould be understood to occur in any order, unless otherwise indicatedor made clear from the context.

The stereolithography system 500 can be an inverted system including amedia source 506 and a build plate 508. In use, the media source 506 cancarry the resin 504, and the build plate 508 can move in a directionaway from the media source 508 as the three-dimensional object 502 isbuilt through layer-by-layer exposure of the second binder in the resin504 to activation light. For example, the stereolithography system 500can include a build chamber 510 defining a working volume 512, in whichthe media source 506 and the build plate 508 can be disposed, and thestereolithography system 500 can include an activation light source 514positioned to direct activation light, as described in greater detailbelow, into the working volume 512 in a direction toward the mediasource 506 and the build plate 508. Continuing with this example, lightfrom the activation light source 514 can be controlled to be incident onthe resin 504 carried by the media source 506 to cross-link and/orpolymerize the second binder in the resin 504 in a predetermined patternto form a layer of the three-dimensional object 502 on a substrate(e.g., the build plate 508 or a previous layer of the three-dimensionalobject 502) while the inverted orientation of the stereolithographysystem 500 can facilitate draining excess resin 504 from thethree-dimensional object 502 and back toward the media source 506.

The stereolithography system 500 can, additionally or alternatively,include one or more heaters 516 in thermal communication with the mediasource 506 and/or the working volume and operable to control thetemperature of the resin 504, e.g., through conduction, forcedconvection, natural convection, radiation, and combinations thereof. Theheaters 516 may, for example, include a resistance heater in thermalcommunication with the media source 506, the build plate 508, or anyother suitable component of the system 500. The heaters 516 may also orinstead include an ambient heater for the working volume 512 above themedia source 506. The one or more heaters 516 may be generally operableto directly or indirectly control a temperature of the resin 504 duringa fabrication process. The stereolithography system 500 can also includeone or more temperature sensors 518 such as thermocouples or the like tofacilitate controlling the heaters to achieve a desired thermal profilewithin the working volume 512, the resin 504, and so forth.

While the working volume 512 can be heated in various different ways toachieve any one or more of the various different advantages describedherein for facilitating stereolithographic fabrication of metal parts,it should be appreciated that certain portions of the stereolithographysystem 500 can be advantageously thermally isolated from the workingvolume 512 and/or from the heaters 516. For example, the activationlight source 514 can be thermally isolated from the working volume 512and/or the heaters 516. Such thermal isolation of the activation lightsource 514 can be useful, for example, for prolonging the useful life ofthe activation light source 514. Additionally, or alternatively, thestereolithography system 500 can include a feedstock source, from whichthe resin 504 can be delivered to the media source 506. The feedstocksource can be thermally isolated from the working volume 512 and/or theheaters 516 to facilitate handling the resin 504. That is, the resin 504can be stored in a substantially solid form. Additionally, oralternatively, given that particles will tend to settle faster in amolten form of the resin 504, thermally isolating the feedstock from thework volume 512 and/or the heater(s) 516 can facilitate storing a usableform of the resin 504 for a longer period of time.

In general, the activation light source 514 can deliver light of awavelength and exposure time suitable to crosslink and/or polymerize thesecond binder of the resin 504. The activation light source 514 can bean ultraviolet light source in implementations in which the secondbinder of the resin 504 undergoes crosslinking and/or polymerizationupon sufficient exposure to ultraviolet light. As a more specificexample, the activation light source 514 can be any one or more ofvarious different ubiquitous light sources that produce light having awavelength of about 300 nm to about 450 nm (e.g., about 405 nm, whichcorresponds to the Blu-ray disc standard). In certain implementations,the activation light source 514 has a wavelength greater than theaverage size of particles suspended in the resin 504, which can reducethe likelihood that the particles will interfere with crosslinkingand/or polymerization of the second binder of the resin 504. Suchreduced interference can, for example, advantageously reduce the amountof light exposure time required to crosslink and/or polymerize thesecond binder in the resin 504. Further, or instead, reducedinterference can enhance resolution by reducing light scattering.

The activation light source 514 can be controllable to provide a patternof light incident on the resin 504. For example, the activation lightsource 514 can include a laser controlled to rasterize an image on theresin 504. As another, non-exclusive example, the activation lightsource 514 can include a digital light processing (DLP) projectorincluding a plurality of micromirrors controllable to create an image onthe resin 504.

Light from the activation light source 514 can pass through a portion ofthe media source 506 that is optically transparent to the light from theactivation light source 514 such that the presence of the media source506 in the light path produces little to no interference with lightdirected from the activation light source 514 to the resin 504 carriedby the media source 506. Thus, for example, in implementations in whichthe activation light source 514 is an ultraviolet light source, theportion of the media source 506 in the path of the activation lightsource 514 can be transparent to ultraviolet light. Further, or instead,in implementations in which the activation light source 514 is disposedoutside of the working volume 512, light from the activation lightsource 514 can pass through a portion of the build chamber 510 that isoptically transparent to the light from the activation source 514 suchthat the presence of the media source 506 in the light path produceslittle to no interference with light directed from the activation lightsource 514 to the resin 504 carried by the media source 506. While themedia source 506 and/or the build chamber 510 can be opticallytransparent to light from the activation light source 514, it should beappreciated that it may be desirable to use the medial source 506 and/orthe build chamber 510 to filter light from the activation light source514.

The stereolithography system 500 can further include a controller 520(e.g., one or more processors) and a non-transitory, computer readablestorage medium 522 in communication with the controller 520 and havingstored thereon computer executable instructions for causing the one ormore processors of the controller 520 to carry out the various methodsdescribed herein. For example, the controller 520 can be incommunication with one or more of the build plate 508, the activationlight source 514, the heater(s) 516, and the temperature sensor 518 tocontrol fabrication of the three-dimensional object 502 based on athree-dimensional model 524 stored on the storage medium 522. In certaininstances, the stereolithography system 500 can further include a cameraand vision system that can detect parameters (e.g., dimensions) of thethree-dimensional object 502 as it is formed, and the storage medium 522can store a digital twin 526 of the three-dimensional object 502 suchthat variations and defects of the three-dimensional object 502 can beevaluated.

In general, the resin 504 can be responsive to light, heat, or acombination thereof controlled by the controller 520 such that thesecond binder can be controllably crosslinked or polymerized. Thus, ascompared to a material in which binders are initially crosslinked orpolymerized, the ability to control crosslinking or polymerization ofthe second binder of the resin 504 can advantageously facilitatecontrolling a shape and, thus, forming a layer of the three-dimensionalobject 502 during a stereolithography process.

In general, the resin 504 can include particles suspended in a mixtureof the first binder and the second binder. As used herein, a binder canbe one or more constituent components removable from the particles at apoint in the fabrication process. Thus, for example, the first bindercan be removable from the particles through a first debinding process,and the second binder can be removable from the particles through asecond debinding process, which can be different from the firstdebinding process and/or temporally separate from the first debindingprocess. Additionally, or alternatively, the first binder and the secondbinder can have different responses to incident light such that, forexample, the first binder can be substantially non-reactive underexposure to wavelengths of light sufficient to crosslink or polymerizethe second binder. Thus, for example, the physical properties of thesecond binder can be changed during a stereolithographic process withoutsignificantly changing the physical properties of the first binder. Moregenerally, it should be appreciated that the physical properties of thefirst binder and the second binder in the resin 504 can be changedthrough the selective and controlled application of energy (e.g., light,heat, or a combination thereof) during a stereolithographic process toaddress different requirements associated with different stages of thestereolithographic process, such as handling (e.g., spreading) the resin504, forming the three-dimensional object 502 layer-by-layer, andfinishing the three-dimensional object 502 into a solid part formedprimarily of the particles suspended in the mixture of the first binderand the second binder.

The suspension of particles may include a dispersion of particles in asolid or molten form of the mixture of the first binder and the secondbinder. It should be appreciated that such a dispersion of the particlescan be uniform or substantially uniform (e.g., varying by less thanabout ±10 percent) within the mixture of the first binder and the secondbinder. More generally, however, it should be appreciated that thedegree of uniformity of the particles can be a function of strengthand/or design tolerances acceptable for the fabrication of thethree-dimensional object 502 and, thus, can include any distribution ofparticles that are substantially spaced apart throughout the mixture ofthe first binder and the second binder.

The first binder and the second binder can be, for example, misciblewith one another such that the mixture of the first binder and thesecond binder is homogenous. Additionally, or alternatively, the firstbinder and the second binder can be immiscible with one another. In suchinstances, the dispersion of the particles in the mixture of the firstbinder and the second binder can be formed by shaking or otherwiseagitating a molten form of the resin 504 prior to or during astereolithography process.

The second binder can be a low molecular weight material (e.g., amonomer or an oligomer), with the low molecular weight indicative of alow degree of crosslinking or polymerization. For example, the secondbinder can have a molecular weight of less than about 5000 g/mol.Continuing with this example, the molecular weight of the second bindercan be increasable from less than about 5000 g/mol to greater than about5000 g/mol (e.g., greater than about 2000 g/mol) under exposure to thewavelength of light sufficient to crosslink or polymerize the secondbinder. The resulting crosslinking or polymerization associated withsuch an increase in molecular weight of the second binder should beunderstood to correspond to curing of the second binder such that theresin 504 takes a relatively stable shape during fabrication of a layerof the three-dimensional object 502.

In certain implementations, the second binder undergoes crosslinking orpolymerization upon exposure to light at a wavelength of about 300 nm toabout 450 nm for a sufficient period of time. Thus, in suchimplementations, the second binder can undergo crosslinking orpolymerization upon exposure to light at a wavelength of 405 nm, whichcorresponds to the Blu-ray disc standard and, thus, is produced using alight source that is ubiquitous.

The first binder and the second binder can have different melttemperatures such that heat can be applied to the resin 504 tofacilitate, for example, handling the resin 504. For example, the firstbinder can have a first melt temperature and the second binder can havea second melt temperature less than or about equal to the first melttemperature. In such instances, the flow of the resin 504 can becontrolled by controlling a temperature of the resin 504 relative to themelt temperature of the first binder. As a more specific example, thefirst binder can have a first melt temperature less than about 80degrees Celsius, and the temperature of the media source 506, the buildplate 508, and/or the working volume 512 can be controlled to be aboveabout 80 degrees Celsius such that the resin 504 is molten prior toreceiving incident light from the activation light source 514.Additionally, or alternatively, the first binder can have a melttemperature above about 25 degrees Celsius such that the resin 504 canbe substantially solid (e.g., in the form of a paste) to facilitatestoring the resin 504 in a stable form for a significant period of time(e.g., multiple weeks). In certain implementations, the concentration ofthe particles suspended in the mixture of the first binder and thesecond binder is such that the resin 504 is a non-Newtonian fluid at 25degrees Celsius.

Additionally, or alternatively, the first binder and the second bindercan have different decomposition temperatures. For example, the firstbinder can have a first decomposition temperature, and the second bindercan have a second decomposition temperature greater than the firstdecomposition temperature such that the second binder can generallywithstand heating to a greater temperature (e.g., after debinding thefirst binder from the three-dimensional object 502).

The first binder can be extractable from the binder system and thesecond binder following exposure of the second binder to a wavelength oflight sufficient to crosslink or polymerize the second binder. Forexample, the resin 504 can be exposed to light from the activation lightsource 514 such that the second binder crosslinks or polymerizessufficiently to at least partially harden to form a stable layer of thethree-dimensional object 502 from which the first binder can ultimatelybe extracted. It should be appreciated that extracting the first binderfrom the three-dimensional object 502 leaves behind a brown part thatcan be subsequently processed (e.g., by debinding the second binder andsintering the remaining particles) to form a completed part.

In general, the first binder can be extractable from the second binderand/or the particles through any of various different processes suitedto the composition of the first binder. For example, the first bindercan include a wax extractable from the second binder by chemicalsolvation in a non-polar chemical following exposure of the secondbinder to wavelengths of light sufficient to crosslink or polymerize thesecond binder. As another, non-exclusive example, the first binder caninclude a plurality of low-molecular weight constituents (e.g., paraffinwax and steric acid), each constituent extractable from the secondbinder by the same chemical solution (e.g., hexane) following exposureof the second binder to wavelengths of light sufficient to crosslink orpolymerize the second binder. Additionally, or alternatively, the firstbinder can include polyethylene glycol extractable from the secondbinder by dissolution by water or alcohols following exposure of thesecond binder to wavelengths of light sufficient to crosslink orpolymerize the second binder. Still further in addition, or in thealternative, the first binder can include a wax extractable from thesecond binder by supercritical carbon dioxide fluid following exposureof the second binder to wavelengths of light sufficient to crosslink orpolymerize the second binder. Yet further in addition, or yet further inthe alternative, the first binder can include a low molecular weightpolyoxymethylene extractable from the second binder by catalyticdebinding in nitric oxide vapor. For example, the polyoxymethylene canmelt at a temperature substantially similar to a temperature at whichthe second binder is photopolymerizable. In certain implementations, thefirst binder includes polyanhydride extractable from the second binderby hydrolysis and dissolution in aqueous solution following exposure ofthe second binder to wavelengths of light sufficient to crosslink orpolymerize the second binder. In some implementations, the first binderincludes a wax thermally extractable from the second binder followingexposure of the second binder to wavelengths of light sufficient tocrosslink or polymerize the second binder. The thermal extraction caninclude, for example, boiling the wax at a temperature at which thesecond binder remains substantially intact (e.g., substantiallyretaining its shape).

The second binder can be removable from the first binder and/or from theparticles through any of various different debinding processes suitablefor one or more constituent components of the second binder. Forexample, the second binder can be debindable by cleaving and/orun-polymerizing the second binder (e.g., through one or more ofhydrolyzing or solvolyzing) following crosslinking or polymerization ofthe second binder. For example, the second binder can include acetaldiacrylate, which can be extractable from the first binder by catalyticdebinding in nitric oxide vapor following exposure of the second binderto a wavelength of light sufficient to crosslink or polymerize thesecond binder. As an additional or alternative example, the secondbinder can include anhydride diacrylate, which can be extractable fromthe first binder by hydrolysis and dissolution in one or more aqueoussolutions following exposure of the second binder to the wavelength oflight sufficient to crosslink or polymerize the second binder. Yetfurther in addition, or further in the alternative, the second bindercan include a saccharide diacrylate (e.g., monosaccharide diacrylate,disaccharide diacrylate, or a combination thereof), each of which can beextractable from the first binder by hydrolysis in one or more aqueoussolutions including a catalyst (e.g., a catalyst including one or morebiological enzymes, such as amylase) for hydrolysis of the crosslinkedor polymerized second binder following exposure of the second binder tothe wavelength of light sufficient to crosslink or polymerize the secondbinder. Additionally, or alternatively, in instances in which the secondbinder is debindable by cleaving and/or un-polymerizing the secondbinder, the first binder can have a high molecular weight (e.g., greaterthan about 5000 g/mol) and exist in a small volume percentage (e.g.,less than about 10 percent) in the resin 504.

The particles suspended in the mixture of the first binder and thesecond binder are solid particles that, in general, can be sintered toform a solid finished part. The particles can include, for example, anyone or more of various different metals. Further, or instead, theparticles can include any one or more of various different ceramics. Tofacilitate producing a solid part with substantially uniform strengthcharacteristics along the part, the solid particles can have the samecomposition and can, additionally or alternatively, have a substantiallyuniform size. In certain instances, the particles can advantageouslyhave an average size that is less than a wavelength of light sufficientto crosslink the second binder, which can have any of various differentadvantages described herein. For example, such a ratio of particle sizeto the wavelength of light can result in shorter times associated withcrosslinking or polymerizing the second binder, given that the particlesare less likely to interfere with incident light that has a longerwavelength than the average particle size.

In general, it is desirable to have a high concentration of theparticles in the resin 504. Such a high concentration can be useful, forexample, for reducing the amount of time and/or energy required tocrosslink or polymerize the second binder. Additionally, oralternatively, such a high concentration can be useful for reducing theamount of time required for debinding the first binder and/or debindingthe second binder. As a specific example of a high concentration, theconcentration (by volume) of the particles in the resin 504 can bewithin +15 percent of the tap density of the particles. As used herein,the tap density of particles is the bulk density of a powder of theparticles after a compaction process and is specified in ASTM B527,entitled “Standard Test Method for Tap Density of Metal Powders andCompounds,” the entirety of which is incorporated herein by reference.

The particles can include modified surfaces such that the particlesexhibit physical or chemical characteristics that differ advantageouslyfrom the underlying material of the particles. For example, theparticles can include chemically functionalized surfaces such assurfaces having a metal oxide coating, which can be useful for resistingcorrosion or other undesired chemical reactions. Additionally, oralternatively, the particles can include functional groups such that theparticles resist settling in the mixture of the first binder and thesecond binder through steric hindrance. In certain instances, underambient conditions (e.g., in air at about 25 degrees Celsius atatmospheric pressure and with relative humidity of 20-80%), theparticles suspended in the mixture of the first binder and the secondbinder can have a timescale of settling of greater than about two weeks,which can facilitate storing the resin 504 in a stable form for a usefulperiod of time. In some instances, the settling time of the particlescan be greater than the amount of time at which the first binder ismolten during the stereolithography process.

The resin 504 can include a photo-absorber (e.g., a Sudan dye) suspendedin the mixture of the first binder and the second binder. Such aphoto-absorber can facilitate, for example, tuning the resin 504 toachieve a particular response (e.g., a curing time for the secondbinder) from activation light from the activation light source 514.

In general, the second binder can be about 10 percent to about 50percent by volume of the total volume of the resin 504. It should beappreciated that the volumetric composition of the resin 504 can be afunction of, among other things, the composition of the first binder andthe second binder. The first binder can include, for example, one ormore of the following: paraffin wax, carnauba wax, stearic acid,polyethylene glycol, polyoxymethylene, oleic acid, and dibutylphthalate. The second binder can include, for example, one or more ofthe following: poly(methyl methacrylate), polyethylene glycoldiacrylate, urethane oligomers functionalized to acrylate groups, epoxyoligomers functionalized to acrylate groups, 1,6-Hexanediol acrylates,or styrene. Additionally, or alternatively, the resin 504 can includeethylene vinyl acetate, a slip agent (e.g., stearic acid), and/or acompatibilizer (e.g., metal stearate (e.g., zinc stearate), stearicacid, or a combination thereof).

In an exemplary formulation, the first binder can include polyethyleneglycol and the second binder can include poly(methyl methacrylate). Forexample, polyethylene glycol can be about 40-90 percent of the combinedweight of the first binder and the second binder and poly(methylmethacrylate) can be about 10-60 percent of the combined weight of thefirst binder and the second binder.

In another exemplary formulation, the first binder can include paraffinwax and the second binder can include a waxy or hydrophobic diacrylateoligomer.

While binder jetting, fused filament fabrication, and stereolithographyprocesses are shown and described above, it will be appreciated that theprinciples of the inventions disclosed herein may be usefully adapted toany other fabrication techniques suitable for depositing multiplematerials for an object, support structure, and interface layer to forma sinterable object with breakaway support structures as contemplatedherein.

FIG. 6 shows a stereolithography system. The stereolithography system600 is generally analogous to the stereolithography system describedabove, except that each layer is cured on a top surface, and the object602 moves downward into a resin 604 while each layer is exposed fromabove to an activation source such as ultraviolet light. In one aspect,the stereolithography system 600 may be configured for multi-materialstereolithography using, e.g. separate resin baths (and a robotic systemfor switching between same), different resins applied with brushes, tapecasters or the like before curing, or any other suitable technique(s),along with any washing or other treatment as needed between individualcuring steps. One suitable system is described by way of non-limitingexample in U.S. Pat. No. 9,120,270 to Chen et al., incorporated byreference herein in its entirety. These or other techniques may be usedto deposit a sinterable build material, an interface layer, and whereappropriate, a support structure, e.g., for sintering support asgenerally contemplated herein.

Other techniques may also or instead be used to create an interfacelayer for breakaway supports on a sinterable object, such as bybrushing, spraying, or otherwise depositing a layer of ceramic particlesor other sinter-resistant material, e.g., in a colloidal suspension orthe like, onto areas of a layer where an interface layer is desired. Forexample, a colloidal suspension of ceramic particles may be depositedonto a surface of the resin 604 before it is cured. In another aspect, aselective embrittlement material or other material that otherwiseprevents or inhibits bonding between the object 602 and an adjacentsupport structure may be used. Suitable control systems, robotics, andthe like may be included and will readily be appreciated by one ofordinary skill in the art, where the details of these systems are notrepeated here. Accordingly, there is disclosed herein astereolithography system 600 having an interface layer tool 660, whichmay include any of the mechanisms described above, or any other toolsuitable for forming an interface layer 662 as contemplated herein foran object fabricated with a stereolithography process.

FIG. 7 shows an interface layer. Support structures are used in additivefabrication processes to permit fabrication of a greater range of objectgeometries, and may generally include print supports (for physicalsupport of an overlying layer during fabrication), debind supports (toprevent deformation during debinding), and sinter supports (to preventdeformation during sintering). For the build materials contemplatedherein-materials that are subsequently sintered into a final part—aninterface layer may usefully be fabricated between an object and thesupport to inhibit bonding between adjacent surfaces of the supportstructure and the object during subsequent processing such as sintering.Thus, disclosed herein is an interface layer suitable for manufacturewith an additive manufacturing system that resists the formation ofbonds between a support structure and an object during subsequentsintering processes.

According to the foregoing, an article 700 of manufacture may include anobject 702 formed of a build material, a support structure 704, and aninterface layer 706, each of which may be deposited or otherwisefabricated using any of the additive fabrication techniques describedherein, or otherwise fabricated or formed into sinterable andunsinterable layers or the like.

The build material of the object 702 may include any of the buildmaterials described herein. By way of general example, the buildmaterial may include a metal injection molding material or a powderedmetallurgy material. More generally, the build material may include asinterable powdered material for forming a final part at a sinteringtemperature, along with a binder system containing one or more bindersretaining the sinterable powdered material in a net shape of the object702 prior to densifying the sinterable powdered material into the finalpart, e.g., after deposition or other shaping with an additivefabrication process. While the object 702 is depicted for simplicity asa single, horizontal layer of material, it will be understood that asurface 708 of the object 702 adjacent to the interface layer 706 mayhave any shape or three-dimensional topography (within the limits of thesystem that fabricated the object 702), including without limitationvertical surfaces, sloped surfaces, horizontal surfaces, shelves,ridges, curves, and so forth, with the interface layer 706 generallyfollowing the surface 708 of the object 702 wherever an unsinterablebarrier between the object 702 and the support structure 704 isnecessary or helpful.

The one or more binders of the build material may include any of a widerange of materials selected to retain the net shape of the object 702during processing of the object 702 into the final part. For example,processing of the object 702 into the final part may include debindingthe net shape to remove at least a portion of the one or more binders,sintering the net shape to join and densify the sinterable powderedmaterial, or some combination of these. To support the net shape in thiscontext, the one or more binders may generally retain the net shapeuntil sufficient sintering strength is achieved through necking ofparticles of the sinterable powdered material.

The sinterable powder of the build material may include a metallicpowder containing any metal(s), metal alloy(s), or combination of theforegoing suitable for sintering. A wide range of such powders are knownin the powdered metallurgy field. Thus, the build material may include apowdered metallurgy material. The sinterable powdered material may, forexample, have a distribution of particle sizes with a mean diameter ofbetween two and fifty microns, such as about six microns, about tenmicrons, or any other suitable diameter. The build material may also orinstead include submicron particles selected to facilitate sintering ofthe sinterable powdered material, such as smaller particles of thepowdered material, particles of a low-temperature sintering material,and so forth. The submicron particles may also or instead include anelement selected for alloying with the sinterable powdered material, orparticles of a strengthening additive, and so forth. In another aspect,the submicron particles of the binder system have a compositionsubstantially identical to the sinterable powdered material and a sizedistribution with a mean particle size at least one order of magnitudesmaller than the sinterable powdered material.

The sinterable powdered material may also or instead include an alloy ofat least one of aluminum, steel, and copper, where the selectiveembrittlement material includes at least one of antimony, arsenic,bismuth, lead, sulfur, phosphorous, tellurium, iodine, bromine,chlorine, and fluorine.

The support structure 704 may generally provide print support, debindsupport, sintering support, or some combination of these for the object702. Print support will generally be positioned vertically belowsurfaces of the object 702, however where vertical support ends or hasnon-horizontal features, the interface layer 706 may also be positionedon the sides of the support structure 704 or otherwise positionedbetween the support structure 704 and the object 702. More generally,the support structure 704 may be positioned adjacent to the surface 708of the object 702 to provide mechanical support during processing of theobject 702 into a final part, where adjacent in this context meansnearby but separated as appropriate by the interface layer 706.

The support structure 704 may be formed of a support material such as asecond material having a shrinkage rate during processing (e.g.,debinding, sintering, or some combination of these) matched to the buildmaterial of the object 702, so that the support material and the buildmaterial shrink at substantially similar rates during debind, duringsintering, or both. For example, the second material may be the buildmaterial, where the use of the interface layer 706 prevents the buildmaterial from sintering across the interface layer. The second materialof the support structure 704 may also or instead contain the ceramicpowder of the interface layer, or some other ceramic powder or otherpowdered material or the like that resists sintering at the sinteringtemperatures used to sinter the build material of the object 702. Forexample, the second material of the support structure 704 may be formedof substantially the same (or exactly the same) composition as theinterface layer 706, or may include the binder system used in the buildmaterial for the object 702. The second binder system of this interfacelayer 706 may, for example, provide a rheology suitable for use in afused filament fabrication process or the like. Thus, the second bindersystem may facilitate suitable flowability, and may retain the shape ofthe interface layer 706 during a debind of the article 700. The secondbinder system may also or instead retain a shape of the interface layer706 during an onset of a thermal sintering cycle at the sinteringtemperature used to sinter the build material of the object 702 into afinal part.

In another aspect, the support material may shrink at a substantiallysimilar rate to the build material during debind and the supportmaterial may shrink at a substantially greater rate than the buildmaterial during sintering. With this shrinkage profile, the supportmaterial can be more specifically configured to shrink at a rate thatmaintains the support structure 704 in contact with the object 702(through the interface layer 706) during a thermal sintering cycle. Thesupport material may also or instead be configured to shrink at a ratethat maintains the support structure 704 in contact with the object 706at least until the object 702 becomes self-supporting during a sinteringprocess for the build material.

In general, the support structure 704 may include a non-planar supportsurface that varies according to the geometry of the object 702 that isbeing supported, and the support structure 704 may have varying z-axisheights below the bottom surface 708 of the object 702 (in amanufacturing coordinate system for planar fabrication of the articleusing, e.g., fused filament fabrication, binder jetting,stereolithography, or any other suitable fabrication systems. Where abottom surface of an object 702 is flat and requires no structuralsupport, an interface layer 706 may nonetheless be usefully employed,e.g., to facilitate separation of the object 702 from a shrink raft,sintering setter, or other substrate used to carry the object 702 duringfabrication into a final part.

The interface layer 706 may generally be disposed between the supportstructure 704 and the surface 708 of the object 702. The interface layer706 may contain a composition that resists bonding of the supportstructure 704 to the surface 708 of the object 702 through the interfacelayer 706 during sintering. For example, the composition of theinterface layer 706 may include a ceramic powder having a sinteringtemperature higher than the build material, or substantially higher thanthe build material (such as a metallic build material). The interfacelayer 706 may also or instead include a preceramic polymer such as anyof a range of organo-silicon compounds that convert into a ceramic uponheat treatment. More specifically, such a preceramic polymer thatdecomposes into a ceramic during sintering at the sintering temperatureof the build material may usefully be employed to form a ceramicinterface layer during sintering. The interface layer 706 may alsoinclude a thermoplastic binder or other suitable material to retain aposition of the ceramic particles within the article. In one aspect, theinterface layer 706 includes a dissolvable material suitable for removalwith a solvent prior to sintering, e.g., in a chemical debind, and theinterface layer 706 also includes a ceramic powder that maintains aphysical separation layer between the first material and the secondmaterial after the dissolvable material is removed.

In one aspect, the interface layer 706 physically excludes the adjacentsupport structure 704 and object 702 forming a physically separatebarrier between the two. For example, the interface layer 706 may beformed of a ceramic powder that has a substantially greater meanparticle size than the sinterable powdered material of the object 702,and the ceramic powder may be disposed in a second binder system thatretains a shape of the interface layer 706, e.g., to prevent mixing orphysical contact between the object 702 and the support structure 704.

In another aspect, the interface layer 706 may be formed between and/orwithin a surface of the object 702, and adjacent surface of the supportstructure 704, or both. As with other interface layers contemplatedherein, this interface layer 706 may generally resist bonding of thesupport structure 704 to the object 702 during a thermal sintering cycleat a sintering temperature for a sinterable powdered material of thebuild material. For example, the interface layer 706 may be formed witha sintering inhibitor that infiltrates the support structure 704 or theobject 702 where they meet. Thus, while illustrated as a discrete layer,it will be understood that the interface layer 706 may overlap with thesupport structure 704 and/or the object 702 without departing from thescope of this description. This type of structure may result, forexample, where a nanoscopic ceramic powder in a colloidal suspension orother suitable carrier is deposited onto the support structure 704 orthe object 702 (or both) before they are placed in contact with oneanother.

For example, a colloidal suspension may be sprayed or jetted ontointerface locations during a binder jetting or fused filamentfabrication process between layers of support structure 704 and anobject 702 to create an unsinterable composition therebetween. Theceramic powder may have a substantially smaller mean particle size thanthe sinterable powdered material of the build material used for formingthe final part. By spraying or jetting the suspension onto the surface,the ceramic powder may be distributed interstitially between particlesof the sinterable powdered material on an outer surface of the supportstructure 704 to resist necking between the support structure 704 andthe sinterable powdered material of the object 702 around the outersurface during sintering at the sintering temperature, thereby providingthe interface layer 706. A variety of suitable dimensions may beemployed. For example, a ceramic powder of the interface layer 706 maycontain ceramic particles having a mean particle size of less than onemicron. The sinterable powdered material of the build material may havea mean particle size of about ten to thirty-five microns. Moregenerally, the ceramic particles have a mean particle size about atleast one order of magnitude smaller than a similarly measured meanparticle size of the sinterable powdered material.

For extrusion-based processes such as fused filament fabrication,particle sizes may usefully be maintained at dimensions substantiallysmaller than an extrusion opening. Thus, for example, in another aspecta powdered metal of a build material may have a mean particle size atleast one order of magnitude smaller than an interior diameter of anextruder of a fused filament fabrication system. Similarly, a powderedceramic of an interface layer may have a mean particle size at least oneorder of magnitude smaller than an interior diameter of an extruder of afused filament fabrication system.

In another aspect, the ceramic particles may have a mean particle sizegreater than a second mean particle size of the sinterable powderedmaterial, e.g., where the interface layer 706 is deposited using a fusedfilament fabrication system having a nozzle that is suitably large forextruding a composition with the ceramic particles. This may include amean particle size at least fifty percent greater than a second meanparticle size of a powdered metal or other powdered material in theobject 702. The ceramic particles may also or instead have a meanparticle size of about five to fifty microns, about five to fortymicrons, or about twenty to thirty microns. The sinterable powderedmaterial may have a mean particle size greater than about thirty-fivemicrons. In another aspect, a powdered metal of the build material mayhave a mean particle size of about fifteen microns and the interfacelayer may include a powdered ceramic with a mean particle size of atleast twenty-five microns.

Other techniques may also or instead be used to form the interface layeras contemplated herein. For example, the interface layer may include aselective embrittlement material selected to introduce crack defectsinto at least one of the support structure and the object at theinterface layer during sintering into the final part. The particularmaterial(s) for selective embrittlement will be system-dependent,however many suitable systems are known in the art. For example, thesinterable powder may include an alloy of at least one of at least oneof aluminum, steel, and copper, and a suitable corresponding selectiveembrittlement material may include at least one of antimony, arsenic,bismuth, lead, sulfur, phosphorous, tellurium, iodine, bromine,chlorine, and fluorine.

In another aspect, the interface layer may include a material having apowdery macrostructure where the material retains the powderymacrostructure while microscopically densifying to match a shrinkagerate of the object during sintering. By way of non-limiting examples,suitable materials may include at least one of aluminum hydroxide andgamma alumina.

More generally, a wide range of materials and material systems mayusefully be employed as the interface layer 706 contemplated herein. Forexample, the interface layer 706 may include at least one of an ironoxide and a ceramic-loaded polymer. The powdered material of the object702 may include a metal powder, and the interface layer may befabricated from a composition that includes a second phase material witha melting point below a sintering temperature of the metal powder toform a meltable interface that melts out of the interface layer as themetal powder achieves a sintering strength during sintering. In anotheraspect, the interface layer 706 may be formed of or include a preceramicpolymer decomposable into a ceramic during sintering. In another aspect,the interface layer 706 may include a ceramic non-reactive with a secondmaterial of the object 702. For example, the second material may includetitanium and the interface layer 706 may include at least one of yttriaand zirconia.

While the interface layer 706 can usefully inhibit bonding of thesupport structure 704 to the object 702 during sintering or otherprocessing, the interface layer 706 and the support structure 704 canalso usefully shrink during processing in a manner that is matched tothe object 702 in order to provide substantially continuous support asneeded during processing. Thus, for example, the interface layer may beformed of a material with a debind shrinkage rate or a sinteringshrinkage rate substantially matching at least one of the first materialof the support structure and the second material of the object underdebind and sintering conditions suitable for at least one of the firstmaterial and the second material. During debind, the primary pathway forshrinkage may be the removal of binder from the system, and the matchingmay include the selection of similar or identical binder systems. Duringsintering, the densification of the powdered material contributessubstantially to shrinkage, and matching may be achieved through the useof similar materials and particle sizes among the different materials ofthe support 702, the interface layer 706, and the object 702.

In one aspect, a first material of the support structure 704 may beconfigured to shrink at a greater rate than a second material of theobject 702, e.g., by using a lighter loading of powdered material, amaterial that sinters more quickly, or the addition of a material thedecomposes or evaporates more quickly during a thermal sintering cycle.By properly configuring these material systems, a support structure 704may be fabricated that self-separates from the object 702 duringsintering, preferably at a time in the sintering process for the object702 to have achieved a self-supporting sintered strength. Thus, thegreater rate may be selected so that the support structure 704 pullsaway from the object 702 concurrently with the second material of theobject 702 sintering to a self-supporting density. In another aspect,the greater rate may be a rate selected to compensate for non-shrinkagein a ceramic material of the interface layer 706 during at least one ofdebind and sintering. That is, where the interface layer 706 does notreduce volume through sintering, the shrinkage rate of the supportmaterial may be increased to prevent mechanical encroachment of theinterface layer 706 into the object 702 during sintering.

In another aspect, while the interface layer 706 is depicted as auniform layer, it will be appreciated that in some instances, e.g.,where an interface layer 706 is captured between two parallelcantilevered arms of an object 702, the use of non-sintering, and thusnon-shrinking, ceramic particles may cause substantial stresses anddeformation. To mitigate this, the interface layer 706 may contain gapsor the like to facilitate shifting or settling as shrinking occurs,provided that the gaps between regions of the interface layer 706 arenot so large that object or support material can sag into the gap duringprinting, debinding, or sintering. Other techniques may be usefullyemployed for similarly captive support structures or the like. Forexample, an interstitial material may be deposited with a shrinkage ratetuned to maintain contact between the support and the object as neededthrough debinding and sintering, while contracting more quickly to pullaway from adjacent surfaces after adequate sintering strength isachieved. In another aspect, a material may be used that degrades andboils off once the object becomes mechanically stable, but beforereaching a full sintering temperature. Alternatively, a material may beadded that melts at a temperature once a part becomes mechanicallystable but before the full sintering temperature.

FIG. 8 shows a method for forming an interface layer for removablesupports. Support structures are commonly used in additive fabricationprocesses to permit fabrication of a greater range of object geometries.For additive fabrication processes that use materials (such as thosecontemplated herein) that are subsequently sintered into a final part,an interface layer can usefully be fabricated between the object andsupport in order to inhibit bonding between adjacent surfaces of thesupport structure and the object during sintering.

As shown in step 801, the method 800 may include providing a model. Thismay include any computerized model of an object for execution by aprinter, or any suitable representation of the object suitable forprocessing into a printer-ready or printer-executable representation.Thus, for example, while g-code is one common representation of machineinstructions for execution by a printer, the g-code may be derived fromsome other model such as computer-aided design (CAD) model, or someother three-dimensional representation such as a three-dimensionalpolygonal mesh or the like. Various techniques for creating computerizedmodels of objects, and for processing such models intoprinter-executable formats, are known in the art and the details are notrepeated here.

In one aspect, the creation of a printer-executable format may includethe identification of portions of an object that require structuralsupport, such as to provide a surface for printing on, or to physicallysupport a structure during debinding and/or sintering into a final part.The resulting support structures may be incorporated into thecomputerized model of the object that is generated for the printer, andmay, where appropriate, specify support materials for fabricating thesupport structures that are different than the build material used bythe printer to fabricate the object.

As shown in step 802, the method 800 may include fabricating a supportstructure for the object based on the computerized model using any ofthe printers described herein. This may, for example, includefabricating the support structure from a first material. By way ofexample, in a method for controlling a printer in a fused filamentfabrication of an object, this may include extruding a support structurefor a portion of the object using a support material.

As shown in step 804, the method 800 may include forming an interfacelayer on a surface of the support structure. This may, for example,include fabricating a discrete layer of material that provides theinterface layer, or this may include modifying or augmenting thefabrication process to form an interface layer within or adjacent to thesupport structure, the object, or both. Thus, as used herein, referencesto “fabricating an interface layer” are intended to refer to a step offabricating a discrete layer of material between a support structure andan object that provides a non-sintering barrier between the two insubsequent processing. For example, fabricating the interface layer (orthe support structure or the object) may include additivelymanufacturing the interface layer (or the support structure or theobject) using at least one of fused filament fabrication, binderjetting, and optical curing of a powder-loaded resin. The phrase“forming an interface layer,” as used herein, is intended to refer morebroadly to any technique for forming a material system that resistsbonding of the support structure to the object through the interfacelayer during sintering. By forming an interface layer as contemplatedherein, the interface layer may thus provide a non-sintering barrierthat results in breakaway or otherwise removable supports aftersintering.

Numerous examples of both techniques (“forming” and “fabricating”) areprovided below. By way of introductory, non-limiting examples,fabricating an interface layer may include depositing a layer of ceramicparticles with an extruder of a fused filament fabrication systembetween an object and a support structure formed of sinterable, powderedmetal in a binder system. On the other hand, forming an interface layermay include this technique, or other techniques that do not involve thefabrication of a discrete material layer such as inkjetting a colloidalsuspension of fine ceramic particles or some other sintering inhibitorinto a layer of a support structure (or an object) so that the inkjettedmaterial penetrates into the structure to create a material system onthe surface of the structure that resists sintering under sinteringconditions for a sinterable, powdered metal of a support structureand/or object.

While the method 800 is shown as an ordered sequence of steps thatinclude fabricating support, forming an interface, and then fabricatingan object, it will be understood that the object, the support structure,and the interface layer may have complex, varying topologies withhorizontal walls, vertical walls, angled walls, curved walls, and allforms of continuous and discontinuous features. Thus, during processing,any one of these steps may be performed first, second, or third, or incertain instances, several may be performed concurrently or in changingpatterns. For example, for a vertical wall, an object may be fabricated,and then the interface layer, and then the support, and the order maythen switch on a return pass of a printing tool so that the support isfabricated first and the object is fabricated last. Or for a nestedsupport structure such as a cantilevered beam, the vertical process mayinclude fabricating an object, then an interface layer, then support,then an interface layer, then the object.

In another aspect, the interface layer may include a finishing materialfor use on some or all of the exterior surfaces of the object.Accordingly, fabricating the interface layer may include fullyencapsulating the object. The material of this interface layer mayinclude a finishing material for the exposed surfaces of the object,e.g., to provide a desired color, texture, strength, toughness,pliability, or other characteristic. For example, the finishing materialmay include an alloying metal having an aesthetic finish, or theinterface layer may include titanium or some other surface strengthener.

In another aspect, the first material of the support structure or theinterface layer, or both, may be formed of a composition includingmicrospheres that controllably collapse under pressure to reduce volume.The fabrication of suitable microspheres is known in the art, and may beused within the support structure and/or interface in a method thatincludes applying pressure to collapse the microspheres to shrink thematerial and separate the support structure from the object, e.g.,during sintering.

In some embodiments, the interface layer may usefully be formed of thefirst material of the support structure so that the entire support andinterface form an unsinterable mass that decomposes into a powder or thelike during sintering.

As noted above, the interface layer may be fabricated using any of theadditive manufacturing techniques described herein such as fusedfilament fabrication, binder jetting, and stereolithography, e.g., wherethe interface layer includes a ceramic medium or a composition with aceramic additive to inhibit bonding between the support structure andthe surface of the object during sintering. Specific techniques may beused with different fabrication processes to form a useful interfacelayer for breakaway supports. For example, in a fused filamentfabrication system, a processor or other controller may be configured tounderextrude at least one of the support structure, a surface of theobject, and the interface layer to reduce a contact area with anadjacent layer, e.g., by using at least one of an increased tool speedand a decreased volumetric deposition rate. Such a printer may also orinstead be configured to reduce a contact area between the interfacelayer and one of the object and the support structure by decreasing anextrusion bead size or increasing a spacing between roads of depositedmaterial. A method for controlling a printer in a fused filamentfabrication of the object may also or instead include extruding aninterface layer adjacent to the support structure using an interfacematerial.

Forming the interface layer may include other techniques. For example,forming the interface layer may include inkjetting a ceramic-loadedslurry onto the support structure (or the object, if the surfaces areinverted, or both) so that ceramic particles in the slurry can penetratethe support structure to inhibit sintering, or optionally so that theslurry can be cured on the surface of the support structure where it isdeposited to create a physical barrier of ceramic particles over thesupport structure. Similarly, a suspension may be deposited onto thesupport structure (or the object), e.g., where the suspension includes amedium that is resistant to sintering at a sintering temperature of thepowdered material. For example, the suspension may include a selectiveembrittlement material that selectively embrittles a bond between thesupport structure and the surface of the object. A variety of suitableselective embrittlement materials are known in the art, and theparticular material(s) will be dependent on the corresponding materialsof the interface layer. Any such materials suitable for the interfacelayer, such as a composition selected to introduce crack defects intothe interface layer, may usefully be employed.

Forming the interface layer may include depositing an interface materialonto the support structure (or the object) using any supplementaldeposition techniques such as by inkjetting, spraying, micropipetting,and painting an interface material onto the support structure as theinterface layer. Forming the interface layer may also or instead includedepositing at least one of the support structure, the interface layer,and the object in a manner that inhibits bonding of the supportstructure to the object while sintering. Forming the interface layer mayalso or instead include depositing at least one of the supportstructure, the interface layer, and the object in a manner that inhibitsmixing with the interface layer. For example, in a fused filamentfabrication context, a small additional z-axis increment may be includedbetween layers to reduce inter-layer fusion and prevent intermingling ofparticles in adjacent layers. In this manner, a film of binder mayeffectively be formed between adjacent layers that inhibits neckformation across the resulting physical barrier. While the binder systemmay eventually be removed initial necking may preferentially occurwithin each layer rather than across layers, so that the interfacesinters to a weaker state to facilitate mechanical removal. In anotheraspect, forming the interface layer may include oxidizing the interfacelayer to inhibit bonding to the second material of the object, such asby selectively oxidizing a surface with a laser in areas where theinterface layer belongs between a structure and a support.

As shown in step 806, the method 800 may include fabricating a layer ofthe object adjacent to the interface layer. In a fused filamentfabrication context, this may include extruding a build material to forma surface of the object adjacent to the interface layer, on a side ofthe interface layer opposing the support structure. The build materialmay be any of the build materials contemplated herein, such as apowdered material for forming a final part and a binder system includingone or more binders.

Fabricating the layer of the object may also or instead includefabricating a surface of the object from a second material adjacent tothe interface layer. The second material may, for example, include apowdered material for forming a final part and a binder system includingone or more binders. The one or more binders may include any of thebinders or binder systems described herein. In general, the one or morebinders may resist deformation of a net shape of the object duringprocessing of the object into the final part, in particular where thisprocessing includes debinding the net shape to remove at least a portionof the one or more binders and sintering the net shape to join anddensify the powdered material. During these processes, the object may gothrough substantial shrinkage and mechanical stresses, and the binder(s)can usefully retain the net shape under these varying conditions.Subsequent sintering aims to yield a densified final part formed of thepowdered material in the second material, e.g., the build material forthe object, where the sintering causes necking between particles of thepowdered material and subsequent fusion of the powdered material into asolid mass without melting to the point of liquefaction. A variety ofsuitable materials are known in the art for various fabricationprocesses as contemplated herein. In one aspect, the first material ofthe support structure may have a similar or substantially identicalcomposition as the second material of the object.

For example, the second material may include a powdered metallurgymaterial. More generally, the powdered material of the second materialmay include a metal powder, a ceramic powder, or any other sinterablematerial or combination of materials. The powdered material may, forexample, have any suitable dimensions for sintering. While this may varyaccording to the type of material, many useful sinterable powderedmaterials have a distribution of particle sizes with a mean diameter ofbetween two and fifty microns. The powdered material may contain any ofa variety of metals or metal alloys. For example, the powdered materialmay include an alloy of at least one of aluminum, steel, and copper,where the composition of the suspension includes at least one ofantimony, arsenic, bismuth, lead, sulfur, phosphorous, tellurium,iodine, bromine, chlorine, and fluorine. In one aspect, the secondmaterial may include an infiltrable powder with at least one of ametallic infiltrant and a ceramic infiltrant.

In one aspect, the binder system may include a single binder, which may,for example, be removable from the object through a pure thermal debind.This may, for example, be useful, e.g., where fabricating the surface ofthe object includes applying the single binder in a binder jettingprocess or in any other context where a single binder system and/orthermal debinding might usefully be employed.

In another aspect, the binder system may include a first binder that isremoved from the second material during a debind prior to sintering,where the binder system includes a second binder that remains in the netshape at an onset of a thermal sintering cycle. The binder system mayalso or instead include a first binder that is removed from the secondmaterial during a debind prior to sintering, where the binder systemincludes a second binder that remains in the net shape through sinteringinto the final part. In this latter case, the second binder may usefullyinclude submicron particles that facilitate sintering of the powderedmaterial. Still more specifically, the submicron particles may includean element or combination of elements selected for alloying with thepowdered material. In another aspect, the submicron particles may have acomposition substantially identical to the powdered material and a sizedistribution with a mean at least one order of magnitude smaller thanthe powdered material.

As shown in step 808, the method 800 may include sending the fabricatedobject to a processing facility. In one aspect, where the entirefabrication process is performed locally, this step may be omitted. Inanother aspect, a service bureau or the like may be maintained toservice multiple printing locations, where objects are printed locally,and then shipped or otherwise transported to the processing facility forone or more of shaping, debinding, and sintering. This latter approachadvantageously permits sharing of resources such as debinding systemsthat use hazardous materials or large, expensive sintering furnaces.

As shown in step 812, the method 800 may include shaping the object.This may, for example, include smoothing to remove printing artifacts,manual or automated comparison to computerized models, e.g., so thatcorrections can be made, or the addition of scoring, through holes, orthe like along interfaces between support structures and an object tomechanically weaken the interface layer.

As shown in step 814, the method 800 may include debinding the object.The details of the debinding process will depend on the type of bindersystem in the materials used for fabrication. For example, the bindersystem may include a first binder and a second binder, where the firstbinder resists deformation of the net shape of the object duringdebinding of the object and a second binder resisting deformation of thenet shape of the object during a beginning of a thermal sintering cyclefor the object. Debinding may include debinding the object to remove thefirst binder using any corresponding debind process such as chemicaldebinding, catalytic debinding, supercritical debinding, thermaldebinding, and so forth. The debinding may also or instead includeheating the object to remove the second binder. In another aspect, thebinder system may include a first binder and at least one other binder,where the first binder forms about 20 percent to about 98 percent byvolume of the binder system, and where debinding includes debinding thefirst binder from the object to create open pore channels for a releaseof the at least one other binder.

As shown in step 816, the method 800 may include sintering the object.This may include any thermal sintering cycle suitable for a powderedmaterial in the object, the support structure, the interface layer, or acombination of these.

As shown in step 818, the method 800 may include removing the supportstructure from the object, e.g., by physically separating the supportstructure and the object along the interface layer. Depending upon thestructure and materials of the interface layer, this may be a simplemanual process of picking up the object, and potentially rinsing orotherwise cleaning the object to remove any powder residue. In anotheraspect, this may require the application of substantial mechanical forceto break the interface layer which, although weaker than the objectand/or support, may nonetheless have substantial strength.

FIG. 9 shows a flow chart of a method for fabricating an object withoverhead supports. As discussed herein, a variety of additivemanufacturing techniques can be adapted to fabricate a substantially netshape object from a computerized model using materials that can bedebound and sintered into a fully dense metallic part or the like.However, during a thermal sintering cycle, unsupported features such asbridges or overhangs may tend to slump and break, particularly where thesupporting binder escapes the material before sintering has yieldedsignificant strength gain. To address this issue, a variety oftechniques are disclosed for supporting an additively manufactured shapeduring subsequent sintering, such as by providing overhead support tosuspend vulnerable features.

As shown in step 901, the method 900 may begin with providing acomputerized model, which may include providing a computerized model inany of the forms described herein.

As shown in step 902, the method 900 may include fabricating an object.In general, this may include fabricating an object having a net shapebased on the computerized model from a build material. The buildmaterial may include a powdered material for forming a final part and abinder system including one or more binders, where the one or morebinders resist deformation of the object during fabricating, debinding,and sintering of the object into the final part. This may, for example,include any of the powdered materials and binder systems describedherein, such as metal injection molding material or the like.Fabricating may, for example, include using an additive manufacturingprocess to fabricate the object such as a fused filament fabricationprocess, a binder jetting process, or optical curing of a layer ofpowder-loaded resin, e.g. with stereolithography.

As shown in step 904, the method 900 may include fabricating aninterface layer such as any of the interface layers described herein,and using any of the fabrication or forming techniques described herein.For example, this may include fabricating an interface layer between theobject and a support structure (which may be an overhead supportstructure or an underlying support structure), where the interface layeris configured to retain a bond between the object and the supportstructure during a first portion of a sintering process, and to separatethe object from the support structure during a second portion of thesintering process after the first portion.

As shown in step 906, the method 900 may include fabricating a supportstructure. In one aspect, this may include fabricating any of a varietyof print or sintering supports such as those discussed herein. Inanother aspect, fabricating the support structure may include forming asupport structure above a surface of the object, where the surface isupwardly vertically exposed so that the support structure can suspendthe surface from above, and where the support structure includes asuperstructure coupled to the surface to support a downward verticalload on the object.

Fabricating the support structure may, for example, include using anadditive manufacturing process to fabricate the support structure suchas a fused filament fabrication process, a binder jetting process, oroptical curing of a layer of powder-loaded resin, e.g. withstereolithography. In another aspect, the support structure may befabricated using other techniques, such as with a supplemental additivefabrication system configured to string filaments or other structuresupwardly from a surface of the object to a superstructure. Thus, forexample, the support structure may include a filament coupled to a topsurface of the object at a location selected to prevent slumping of theobject during at least one of debind and sintering. The filament may,for example, form a spring coupling the top surface of the object to thesuperstructure with a spring force that varies according to a length ofthe spring. The filament may couple to a frame of the superstructure.Using this general support strategy, generalized support structures maybe formed that provide removable overhead support while permittingunderlying support to be removed early in downstream processing, e.g.,through a chemical debinding process.

Fabricating the support structure may also or instead includefabricating a second support structure below a location where thesuperstructure couples to the surface of the object. Fabricating thesupport structure may also or instead include fabricating a verticalretaining wall separated from a substantially vertical surface of theobject by an interface layer that resists bonding of the verticalretaining wall to the substantially vertical surface of the object. Theretaining wall may, for example, resist slumping of a thin wall of theobject, provide an attachment for an overhead support, or otherwisesupport the object or related structures during subsequent processing.

As previously noted, it may be useful to match or otherwise coordinateshrinkage rates among materials. Thus, for example, the frame may befabricated from a material selected to shrink at a predetermined rateduring a debind and sintering of the object, e.g., so that the overheadsupports continue to provide adequate (but not excessive) force onsupported structures. Similarly, the filament may be fabricated from amaterial selected to shrink at a predetermined rate during a debind andsintering of the object.

As shown in step 908, the method 900 may include sending the fabricatedobject to a processing facility. In one aspect, where the entirefabrication process is performed locally, this step may be omitted. Inanother aspect, a service bureau or the like may be maintained toservice multiple printing locations, where objects are printed locally,and then shipped or otherwise transported to the processing facility forone or more of shaping, debinding, and sintering. This latter approachadvantageously permits sharing of resources such as debinding systemsthat use hazardous materials or large, expensive sintering furnaces.

As shown in step 912, the method 900 may include shaping the object.This may, for example, include smoothing to remove printing artifacts,manual or automated comparison to computerized models, e.g., so thatcorrections can be made, or the addition of scoring, through holes, orthe like along interfaces between support structures and an object tomechanically weaken the interface layer.

As shown in step 914, the method 900 may include debinding the object toprovide a brown part. The details of the debinding process will dependon the type of binder system in the materials used for fabrication. Forexample, the binder system may include a first binder and a secondbinder, where the first binder resists deformation of the net shape ofthe object during debinding of the object and a second binder resistsdeformation of the net shape of the object during a beginning of athermal sintering cycle for the object. Debinding may include debindingthe object to remove the first binder using any corresponding debindprocess such as chemical debinding, catalytic debinding, supercriticaldebinding, thermal debinding, and so forth. The debinding may also orinstead include heating the object to remove the second binder. Inanother aspect, the binder system may include a first binder and atleast one other binder, where the first binder forms about 20 percent toabout 98 percent by volume of the binder system, and where debindingincludes debinding the first binder from the object to create open porechannels for a release of the at least one other binder.

As shown in step 916, the method 900 may include sintering the object toprovide a final part. This may include any thermal sintering cyclesuitable for a powdered material in the object, the support structure,the interface layer, or a combination of these.

As shown in step 918, the method 900 may include removing the supportstructure from the object, e.g., by physically separating the supportstructure and the object along the interface layer. Depending upon thestructure and materials of the interface layer, this may be a simplemanual process of picking up the object, and potentially rinsing orotherwise cleaning the object to remove any powder residue. In anotheraspect, this may require the application of substantial mechanical forceto break the interface layer which, although weaker than the objectand/or support, may nonetheless have substantial strength. Whereoverhead supports are used, the support structure may usefully employ acombination of different interfaces that either fully or partiallyinhibit bonding within different regions of the interface, e.g., so thatoverhead supports can remain at least partially intact until sinteringto full strength while print supports and the like completely detachduring sintering.

FIG. 10 shows an object with overhead support. In general, an article ofmanufacture described herein may include an object with overheadsupports fabricated using the techniques described above. Thus, there isdisclosed herein an article 1000 comprising an object 1002 formed of abuild material such as any of the build materials described hereinincluding a powdered material for forming a final part and a bindersystem including one or more binders, where the one or more bindersresist deformation of the object during fabricating, debinding, andsintering of the object 1002 into the final part. The article 1000 mayinclude a bottom support 1004 providing vertical support from asubstrate 1006 below the build material during fabrication of the object1002 in an additive fabrication process. An interface layer such as anyof the interface layers described above may be formed between the object1002 and the bottom support 1004. The article 1000 may also include atop support 1008 coupled to an upwardly vertically exposed surface 1010of the object 1002, the top support 1008 providing vertical supportagainst downward deformation of the object 1002 during at least one ofdebinding and sintering. The top support 1008 may, for example, includea number of filaments or the like coupled to a superstructure 1012 suchas a frame, box, or other structure providing attachment points 1014above the object 1002.

An interface layer may also or instead be formed between the object 1002and the top support 1008, where the interface layer is configured toretain a bond between the object and the top support during a firstportion of a sintering process, and where the interface layer isconfigured to separate the object from the top support during a secondportion of the sintering process after the first portion, e.g., wherethe object 1002 has reached a self-supporting strength.

FIG. 11 shows a cross-section of an object on a shrinking substrate. Asdescribed above, a variety of additive manufacturing techniques can beadapted to fabricate a substantially net shape object from acomputerized model using materials that can be debound and sintered intoa fully dense metallic part or the like. However, during debinding andsintering, the net shape may shrink as binder escapes and a basematerial fuses into a dense final part. If the foundation beneath theobject does not shrink in a corresponding fashion, the resultingstresses throughout the object can lead to fracturing or other physicaldamage to the object resulting in a failed fabrication. To address thisissue, a variety of techniques are disclosed for substrates and buildplates that contract in a manner complementary to the object duringdebinding and sintering.

An object 1102 fabricated from a sinterable build material willgenerally shrink as debinding and sintering occur. A support structure1104 for the object 1102 may also usefully shrink at a similar oridentical rate engineered to provide structural support to the object1102 as needed during, e.g., debinding and sintering. Sintering setters1106 or other prefabricated substrates may also be used when sinteringto reduce deformation, e.g., as a result of physical displacement ofsurfaces of the shrinking object relative to an underlying surface asthe part shrinks and various part surfaces drag along. While this maywork for certain object shapes and sizes, the planar contraction withina sintering setter 1106 may not accommodate the range of parts thatmight be fabricated with an additive manufacturing system. As such, ashrinking substrate 1108 may be used, either on a sintering setter 1106or some other surface, to ensure that a surface under the object 1102shrinks in a manner consistent with the object 1102 to mitigate or avoidobject deformation. In one aspect, the shrinking substrate 1108 may befabricated with the build material used to fabricate the object 1102, orwith another material having a matched shrinkage profile duringdebinding, sintering, or both. The object 1102 may be separated from theshrinking substrate 1108 and the support structure 1104 using aninterface layer such as any of the interface layers described herein.

FIG. 12 shows a top view of an object on a shrinking substrate. Whilethe shrinking substrate 1208 may nominally have a shrinkage rate matchedto the object 1202, the surface of the object 1202 where it mates withthe shrinking substrate 1208 may actually have varying shrinkageproperties as a function of the three-dimensional shape of the object1202. This may be addressed by creating a number of independent rafts orshrinking substrates 1208 for different contact surfaces of the object1202, which may then be coupled to one another by tie bars, straps, orthe like that are configured to shrink and that draw the rafts towardone another in a manner that matches the shrinkage of the object 1202 asdebinding and sintering occurs. In one aspect, a convex hull of aprojection of the object 1202 onto the shrinking substrate 1208 providesa shape that shrinks in a manner consistent with the object 1202. Thus,a shrinking substrate 1208 may usefully be fashioned by determining aconvex hull of a projection of the object 1202 and offsetting thisconvex hull to provide a margin 1210 around the object 1202 formechanical stability. The shrinking substrate 1208 may also usefully beprovided with perforations 1212 in any suitable size, shape, andarrangement to permit drainage of a chemical solvent or the like fromareas within the projection that are bounded on all sides the by object1202 and bounded on the bottom by the shrinking substrate 1208.

FIG. 13 is a flowchart of a method for fabricating shrinkable supportstructures.

As shown in step 1304, the method 1300 may include providing a base forfabricating an object. The base may, for example, include a build plate,a sintering setter, or any other suitable support for an object to befabricated using techniques contemplated herein. The base may optionallybe a shrinking base that shrinks during debinding and/or sintering, orthe base may be a reusable base that can be returned to a printer afterpost-processing.

As shown in step 1306, the method 1300 may include providing a supportstructure such as any of the shrinkable substrates contemplated herein.This may, for example, include fabricating the support structure on abuild plate formed of a material that is itself debindable andsinterable, e.g., that shrinks with the object during sintering. Wherethe support structure is a build plate, the method 1300 may includefabricating a build plate for use as the support structure by injectionmolding the build plate with a second material having at least one of adebind shrinkage rate and a sintering shrinkage rate matching the buildmaterial used to fabricate the object. Where the substrate is fabricatedlocally, providing the support structure may include fabricating asubstrate for the object from a second material having at least one of adebind shrinkage rate and a sintering shrinkage rate matching the buildmaterial.

As noted above, the substrate may include two or more independentsubstrate plates coupled by a number of tie bars that move theindependent substrate plates together at a rate corresponding to ashrinkage of the object during at least one of debind and sintering.Where the object has two or more discrete and separate contact surfacesin a plane along a top surface of the substrate, the substrate mayinclude two or more corresponding separate substrate regions formedabout a projection of each of the two or more discrete and separatecontact surfaces, and the substrate may include at least one tie bar,strap, or similar structure coupling the two or more discrete andseparate contact surfaces to one another in order to facilitate amovement of the corresponding separate substrate regions in a mannergeographically matched to a motion of the two or more discrete andseparate contact surfaces during at least one of debind and shrinkage.In another aspect, a shape of the substrate may be based upon a convexhull of a projection of the object into a plane of a build plate thatreceives the object during fabrication. As described above, the shapemay, for example, be a shell or outline uniformly displaced by apredetermined offset from the convex hull of the projection. An interiorregion, e.g., a region within the surface of the substrate enclosed bywalls of the object fabricated thereon, may contain an opening tofacilitate drainage of chemical solvents or the like during subsequentprocessing. Thus, the substrate may have an opening with a shape basedon interior walls of the object, or derived from a predetermined inwardoffset from a boundary of the projection of the convex hull of theobject.

In addition to providing shrinkable substrates, providing a supportstructure may include providing other support structures describedherein. For example, providing a support structure may includefabricating a structural support for at least one of a bridge or anoverhang in the object from a second material having at least one of adebind shrinkage rate and a sintering shrinkage rate matching the buildmaterial. For these support structures, interface layers as contemplatedabove may usefully be employed, and the support structure may befabricated from a support material such as a ceramic powder that doesnot solidify during sintering, optionally along with a binder systemthat shrinks with the build material of the object.

As shown in step 1308, the method 1300 may include providingperforations in the support structure, such as prefabricatedperforations in a prefabricated support structure, or a fixed orvariable pattern of perforations where the support structure isfabricated specifically for an object. In general, the substrate mayusefully incorporate a plurality of perforations or the like through thesubstrate and positioned to provide a drainage route through thesubstrate for a debind solvent. While straight, vertical through holesmay conveniently be employed, other configurations are also possible.Thus, for example, the plurality of perforations may extend from a topsurface of the substrate to a bottom surface of the substrate withinregions of the substrate where an adjacent layer of the object does notvertically cover the substrate, or the perforations may extend from atop surface of the substrate to one or more side surfaces of thesubstrate, e.g., to provide a horizontal drainage path toward exterioredges of the projection of the substrate (or to any other usefullocation or combination of locations). The perforations may, forexample, be positioned within a region of the substrate enclosed in anx-y plane of the substrate by a vertical wall of the object extending ina z-axis from the top surface of the substrate and surrounding theregion of the substrate. In one aspect, the substrate may be fabricatedwith a regular pattern of perforations independent of a shape of anobject fabricated thereupon. In another aspect, perforations may beomitted below the object (e.g., to avoid perforation-based surfaceartifacts on the object), such that the substrate forms a continuous,closed surface below a projection of the object into a plane of a buildplate that receives the object during fabrication.

As shown in step 1310, the method 1300 may include fabricating aninterface layer. In general, interface layers may usefully beincorporated between the shrinking substrate and the object, or betweenthe object and other support structures, or between the shrinkingsubstrate and a build plate, sintering setter, or other base thatcarries the object.

As shown in step 1312, the method 1300 may include fabricating an objecton the shrinking substrate. As described above, this may for exampleinclude fabricating an object from a build material on the supportstructure (including the shrinking substrate), where the object has anet shape based on a computerized model, where the build materialincludes a powdered material for forming a final part and a bindersystem including one or more binders, where the one or more bindersresist deformation of the object during a fabrication, a debinding, anda sintering of the object into the final part, and where the supportstructure is configured to match a shrinkage of the object during atleast one of the debinding and the sintering.

As shown in step 1314, the method 1300 may include post-processing suchas any of the shaping, debinding, sintering, or finishing stepsdescribed herein.

According to the foregoing, there is also disclosed herein an additivefabrication system for fabricating an object on a shrinking substrate.This system may, for example, include a build plate, a supply of buildmaterial, and an additive fabrication system. The build material mayinclude any of the build materials described herein, such as a powderedmaterial for forming a final part and a binder system including one ormore binders, where the one or more binders resist deformation of thebuild material during fabricating, debinding, and sintering of the buildmaterial into the final part. The additive fabrication system may be anyof the additive fabrication systems contemplated herein, and may beconfigured to fabricate an object on the build plate from the buildmaterial, where the additive fabrication system imparts a net shape tothe build material based on a computerized model and the additivefabrication system is configured to provide a build surface such as ashrinking substrate having a shrinkage rate matching at least one of adebind shrinkage rate and a sintering shrinkage rate of the buildmaterial.

As discussed above, the build surface may include a preformed substrate,or the build surface may be a shrinking substrate fabricated for aspecific object. For example, the build surface may include a shrinkingsubstrate fabricated below a convex hull of a projection of the objectinto a plane of the build plate, and more specifically having a shapebased on the convex hull of the projection of the object into the planeof the build plate. The system may also include a debinding station toremove at least one of the one or more binders from the build materialin the object and a sintering oven to heat the object to form bondsbetween particles of the powdered material. The additive fabricationsystem may, for example, include at least one of a binder jet system ora fused filament fabrication system.

There is also disclosed herein an article of manufacture including abase plate with a shrinkable substrate and an object formed of asinterable build material such as any of those described herein.

FIG. 14 shows a flow chart of a method for independently fabricatingobjects and object supports. Additive fabrication systems generally usesupport structures to expand the available range of features andgeometries in fabricated objects. For example, when a vertical shelf orcantilever extends from an object, a supplemental support structure maybe required to provide a surface that this feature can be fabricatedupon. This process may become more difficult when, e.g., a part will besubjected to downstream processing steps such as debinding or sinteringthat impose different design rules. To address these challenges andprovide a greater range of flexibility and processing speed, it may beuseful in certain circumstances to independently fabricate the objectand support structures, and then assemble these structures into acomposite item for debinding and sintering. This approach alsoadvantageously facilitates various techniques for spraying, dipping, orotherwise applying a release layer between the support structure and thepart so that these separate items do not become fused together duringsintering.

As shown in step 1404, the method 1400 may include fabricating a supportstructure for an object from a first material. Fabricating the supportstructure may, for example, include additively manufacturing the supportstructure using at least one of fused filament fabrication, binderjetting, and optical curing of a powder-loaded resin.

As shown in step 1406, the method 1400 may include fabricating theobject. This may include fabricating the object from a second material,the object including a surface positionable adjacent to and supportableby the support structure, where the second material includes powderedmaterial for forming a final part. A binder system may include a firstbinder that resists deformation of a net shape of the object duringfabrication and a second binder that resists deformation of the netshape of the object during sintering of the object into the final part.

In one aspect, the first material of the support structure and thesecond material of the object may be substantially similar or includeidentical compositions. Thus, the first material and the second materialmay be deposited from a single source, such as by extruding a singlebuild material for both from a single extruder of a fused filamentfabrication system. The first material and the second material may alsoor instead have substantially matched shrinkage rates during debindingand sintering of the first material. The powdered material of the firstmaterial may include a metal powder, a ceramic powder, or any sinterablematerial. The binder system may include a first binder and a secondbinder, where the first binder is selected to resist deformation of thenet shape of the object during debinding of the object and a secondbinder selected to resist deformation of the net shape of the objectduring a thermal sintering cycle used to sinter the object.

In general, fabricating the object may include additively manufacturingthe object using at least one of fused filament fabrication, binderjetting, and optical curing of a powder-loaded resin.

As shown in step 1408, the method 1400 may optionally include removingthe first binder of the object. By performing this step on the object,and possibly the support structure where similar binder systems areused, subsequent processing may be performed more quickly than if, forexample, the object and support structure are assembled together and thesurfaces through which debinding might otherwise occur become occluded.

As shown in step 1410, the method may include applying an interfacelayer to the object or the support structure (or both). Applying theinterface layer may include applying the interface layer using at leastone of fused filament fabrication, binder jetting, and optical curing ofa powder-loaded resin. The interface layer may, for example, include anyof the interface layers contemplated herein, and may generally resistbonding of the support structure to the object during sintering.

In one aspect, applying the interface layer may include applying aninterface layer to a least one of the support structure and the objectat a location corresponding to the surface of the object positionableadjacent to and supportable by the support structure. Applying theinterface layer may also or instead include applying a ceramic-loadedslurry onto the support structure or applying a ceramic suspension ontothe support structure. A variety of other techniques may also or insteadbe used to apply the interface layer. For example, applying theinterface layer may include spraying the interface layer onto at leastone of the support structure and the object. Applying the interfacelayer may include dipping at least one of the support structure and theobject into an interface material. Applying the interface layer mayinclude micropipetting the interface layer onto at least one of thesupport structure and the object.

As shown in step 1412, the method may include assembling the supportstructure and the object together into an assembled workpiece. This mayinclude assembling the pieces so that the surface of the object ispositioned adjacent to and supported by the support structure. This mayalso include positioning the assembled workpiece on a build plateconfigured to shrink at a substantially equal rate to the object duringat least one of debinding and sintering.

As shown in step 1414, the method 1400 may include debinding theassembled workpiece, such as by using any of the debinding techniquescontemplated herein.

As shown in step 1416, the method 1400 may include sintering theassembled workpiece, such as by using any of the sintering techniquescontemplated herein.

As shown in step 1418, the method 1400 may include finishing the object,which may include disassembling the sintered workpiece to retrieve thefinal part, along with any other appropriate finishing orpost-processing steps.

FIG. 15 shows a flow chart of a method for fabricating multi-partassemblies. By forming release layers between features such as bearingsor gear teeth, complex mechanical assemblies can be fabricated in asingle additive manufacturing process. Furthermore, by using supportstructures that can be dissolved in a debinding step, or that otherwisedecompose into a powder or other form, support material can usefully beremoved from these assemblies after sintering.

In one aspect, a non-structural support at the interface, e.g. a purebinder that does not sinter into a structural object, may be used tofacilitate the additive manufacture of nested parts. For example, acomplete gear box or the like may be fabricated within an enclosure,with the surfaces between gear teeth fabricated with a non-sinteringbinder or other material. In one aspect, critical mechanical interfacesfor such mechanical parts may be oriented to the fabrication process,e.g., by orienting mating surfaces vertically so that smallerresolutions can be used. More generally, the capability to printadjacent, non-coupled parts may be used to fabricate multiple physicallyrelated parts in a single print job. This may, for example, includehinges, gears, captive bearings, or other nested or interrelated parts.Non-sintering support material may be extracted, e.g., using anultrasonicator, fluid cleaning, or other techniques after the object issintered to a final form. In an aspect, the binder is loaded with anon-sintering additive such as ceramic or a dissimilar, higher sinteringtemp metal.

This general approach may also affect the design of the part. Forexample, axles may employ various anti-backlash techniques so that thesintered part is more securely retained during movement and use.Similarly, fluid paths may be provided for fluid cleaning, and removalpaths may be created for interior support structures. This technique mayalso be used to address other printing challenges. For example, supportstructures within partially enclosed spaces may be fabricated forremoval through some removal path after the object is completed. If thesupport structures are weakly connected, or unconnected, to thefabricated object, they can be physically manipulated for extractionthrough the removal path. In an aspect, parts may be “glued” togetherwith an appropriate (e.g., the same) MIM material to make larger partsthat essentially have no joints once sintered.

A method 1500 for fabricating multipart components is now described ingreater detail.

As shown in step 1504, the method 1500 may include fabricating a firstobject from a first material. The first material may include any of thematerial systems described herein, such as a powdered material and abinder system, the binder system including a first binder that resistsdeformation of a net shape of the first material during fabrication anda second binder that resists deformation of the net shape of the firstmaterial during sintering of the first material into a final part. Thepowdered material may, for example, include a powdered metal.

Fabricating, as contemplated herein for this step and subsequent steps,may include fabricating using a fused filament fabrication process, abinder jetting process, or a stereolithography process, as well ascombinations of these and other supplemental additive and subtractivefabrication processes described herein.

As shown in step 1506, the method 1500 may include applying an interfacelayer to a first surface of the first object. The interface layer mayusefully reduce to a powder during sintering of the first material,e.g., so that the material can be removed after fabrication. Theinterface layer may, for example, include a powdered ceramic having asubstantially higher sintering temperature than the powdered materialused in the first object (and second object, below). In general,applying the interface layer may include fabricating the interface layerusing the techniques noted above. Applying the interface layer may alsoor instead include one or more of inkjetting, micropipetting, andpainting an interface material onto the first surface to form theinterface layer. In this context, the interface material may, forexample, include a ceramic-loaded polymer, a ceramic-loaded suspension,a ceramic-loaded slurry, or any other ceramic and carrier combinationsuitable for distribution onto one of the object surfaces to form aninterface layer.

As shown in step 1508, the method may include fabricating a secondobject. This may include fabricating a second surface of the secondobject from a second material at a location adjacent to the interfacelayer and opposing the first surface of the first object, where thesecond object is structurally independent from and mechanically relatedto the first object, and where the interface layer resists bonding ofthe first surface to the second surface during sintering. It will beunderstood that fabricating the second object may be performed prior to,after, or concurrently with fabricating the first object. Thus, whilethe method 1500 described herein generally contemplates concurrentfabrication of interrelated mechanical assemblies, this may also orinstead include separate manufacture and assembly of parts as describedabove with reference to FIG. 14. These techniques may thus be used aloneor in any useful combination to facilitate the fabrication of complexmechanical assemblies based on computerized models using sinterable,metal-bearing build materials.

The materials of the first object and the second object, e.g., an objectand a support for the object, or an object and a complementarymechanical part such as a mating gear, may have generally complementaryproperties. The first material (of the support) and the second material(of the object) may be supplied from a single source of build material,such as an extruder of a fused filament fabrication system or acontainer of stereolithography resin, and may have a substantiallycommon composition. The first material and the second material may alsoor instead have substantially similar shrinkage rates during a thermalsintering cycle.

The first object and the second object may be mechanically orstructurally related in a number of different ways. For example, thefirst object and the second object may form a multi-part mechanicalassembly such as a hinge, a gear set, a bearing, a clamp, and so forth.For example, the first object and the second object may includecomplementary gears, or one of the first object and the second objectmay include an axel or a bearing. The multi-part assembly may alsoinclude one or more parts moving within a casing. Where the casingencloses the multi-part mechanical assembly, or otherwise requiresinternal print support, sinter support or the like, an exit path may beprovided. Thus, the method 1500 may include providing a physical exitpath from the casing for a third material of the interface layer, eitherby printing the casing with the physical exit path or by adding thephysical exit path with a subtractive tool after the casing is printed.The method 1500 may also or instead include providing a physical exitpath within the multi-part mechanical assembly for extraction of asupport material. To facilitate removal in this manner, the supportmaterial may reduce to a powder during sintering of the first material.In another aspect, the support material may be a dissolvable material,and the method 1500 may include dissolving the support material in asolvent and removing the support material and solvent through thephysical exit path. This may, for example, occur during a chemicaldebind, or as an independent step for support removal.

As shown in step 1514, the method 1500 may include debinding the firstobject and the second object using any of the debinding techniquescontemplated herein.

As shown in step 1516, the method 1500 may include sintering the firstobject and the second object using any of the sintering techniquescontemplated herein.

As shown in step 1518, the method 1500 may include finishing the firstobject and the second object using any of the techniques contemplatedherein.

FIG. 16 illustrates a mechanical assembly in a casing. In general, themechanical assembly 1600 may include any number of interrelated partssuch as gears 1602, axels 1604, springs 1606, moving arms 1608, and soforth. The mechanical assembly 1600 may include a casing 1610 that isfabricated, e.g., concurrently with the mechanical assembly 1600 usingan additive fabrication process, and that encloses some or all of themoving parts of the mechanical assembly 1600. The casing 1610 may also,where useful, incorporate passages to exterior surfaces for switches,buttons, or other controls, or for more generally coupling to movingparts outside the casing 1610 through the walls of the casing 1610. Asdescribed above, individual components of the mechanical assembly 1600may be fabricated in place, e.g., in intimate mechanical engagement withone another. In order to maintain at least partial mechanicalindependence, individual components of the mechanical assembly 1600 mayalso by physically separated using an interface layer as describedabove. However, the material of the interface layer, as well as anysupport structures or the like used to fabricate objects inside thecasing 1610, may require removal after fabrication in order for thecomponents of the mechanical assembly to function as intended. Thus, thecasing 1610 may usefully incorporate a physical exit path 1612 in orderto facilitate the ingress of solvents or cleaning fluids, and the egressof such fluids along with materials of the interface layers and/orsupport structures within the casing 1610.

A second passageway 1614 may also be provided, which facilitatesflushing of the interior of the casing 1610 by providing a solvent orother cleaning fluid or the like through one passageway, e.g., thephysical exit path 1612 and out another passageway, e.g. the secondpassageway 1614.

In another aspect, modular support structures 1620 may be fabricatedwithin the casing 1610, with individual elements of the modular supportstructures 1620 separated by an interface layer to permit disassemblyand individual removal. Thus, the physical exit path 1612 may alsoprovide a passageway for removal of modular support structures 1620, asdiscussed in greater detail below.

FIG. 17 shows a flow chart of a method for fabricating removable sintersupports. Additive fabrication systems such as those described hereingenerally use support structures to expand the available range offeatures and geometries in fabricated objects. For example, when anoverhang or cantilever extends from an object, a supplemental supportstructure may be required to provide a surface that this feature can befabricated upon. This process may become more difficult when a surfacerequiring support is enclosed within a cavity inside an object beingfabricated. Techniques are disclosed herein for fabricating supportsthat can be removed from within cavities in an object.

As shown in step 1704, the method 1700 may begin with fabricating anobject with a cavity. For example, this may include fabricating anobject from a build material using an additive fabrication process,where the object has a cavity and a passageway (such as the cavity andthe physical exit path described above). The cavity may generallyinclude an interior surface requiring support during fabrication, suchas an interior wall of the cavity or a surface of an independentmechanical part within the cavity. The passageway may generally providean open passage between the cavity and an exterior environment for theobject. In another aspect, the cavity may be fabricated with a pluralityof passageways arranged to facilitate flushing fluid in from a first oneof the passageways through the cavity and out through a second one ofthe passageways.

In another aspect, fabricating the object may include fabricating anobject from a build material using an additive fabrication process,where the build material includes a powdered build material and a bindersystem, the binder system including a first binder that resistsdeformation of a net shape of the object during fabrication and a secondbinder that resists deformation of the net shape of the object duringsintering of the object into a final part, and where the object has acavity and a passageway, the cavity including an interior surfacerequiring support during fabrication and the passageway providing anopen passage between the cavity and an exterior environment for theobject.

In general, the object may be fabricated using any of the techniques,and with any of the build materials, described herein. Thus, forexample, the build material may include a powdered material (such as ametallic powder) and a binder system, the binder system including afirst binder that resists deformation of a net shape of the objectduring fabrication and a second binder that resists deformation of thenet shape of the object during sintering of the object into a finalpart.

As shown in step 1706, the method 1700 may include fabricating a supportstructure for the interior surface within the cavity. In one aspect, thesupport structure may include a composite support structure formed froma plurality of independent support structures such as the modularsupport structures described above, which may be configured tocollectively provide support to the interior surface to satisfy afabrication rule for the build material. Although the passageway may besmaller than the composite support structure, each of the independentsupport structures may be shaped and sized for individual removal fromthe cavity through the passageway, thus facilitating removal of largesupport structures through a small passageway in an enclosure such asthe cavity. For example, the composite support structure may have ashape with dimensions collectively too large to pass through a smallestwidth of the passageway. Or, for example, where the passageway forms atortuous path, the passageway may not provide a draw path for removal ofthe composite support structure as a rigid object, while independentsupport structures that make up the composite support structure may beremoved one at a time through the passageway. Similarly, in thiscontext, the term cavity is intended to include any partially enclosedor wholly enclosed space with an interior volume that contains, or mightcontain, a support structure that cannot, as a composite structure, beextracted through a passageway into the cavity from an exterior space.

In another aspect, the support structure may be fabricated from apowdered support material in a matrix such as any of the powderedmaterials and binders or the like described herein. This may facilitatea range of other removal techniques. For example, the method 1700 mayinclude dissolving the matrix during a debind (as described below), orremoving the matrix during sintering of the object. The method 1700 mayalso or instead include reducing the support structure to a powder byremoving the matrix through any suitable means. Where the supportstructure can be reduced to a powder, the method 1700 may furtherinclude removing the powdered support material from the cavity, e.g., byflushing with a gas, a liquid, or any other suitable cleaning medium.

As shown in step 1708, the method may include fabricating an interfacelayer. This may, for example, include fabricating an interface layerbetween the support structure and a supported surface, or between thesupport structure and another surface such as an interior wall of thecavity that provides the support (through the support structure) for thesupported surface, or between one of the plurality of independentsupport structures and an adjacent portion of the interior surface ofthe cavity. This may also usefully include fabricating an interfacelayer between each of the plurality of independent support structures tofacilitate disassembly and removal of each of the plurality ofindependent support structures from the cavity through the passageway.It will be understood that while illustrated as occurring afterfabricating the support structure, fabrication of the interface layerwill occur in-between layers of the independent support structures, andas such, may be performed before, during, and/or after fabrication ofthe independent support structures as necessary to render a compositesupport structure that can be disassembled and removed.

In general, one or more interface layers may be fabricated from any ofthe interface materials contemplated herein. For example, the interfacelayer may be formed of an interface material including a ceramic powder,or any other interface material that resists bonding of the supportstructure to the interior surface of the object during sintering.

As shown in step 1710, the method 1700 may include removing the supportstructure, e.g., using any of the techniques described herein.

As shown in step 1714, the method 1700 may include debinding the object.In one embodiment, the support structure is a fabrication supportstructure (as distinguished, e.g., from a sintering support structure),and the interface layer is removable with the debind. In thisarrangement, the method 1700 may include removing the support structureafter debinding (e.g., after the interface layer has been removed) andbefore sintering.

As shown in step 1716, the method 1700 may include sintering the object,e.g., using any of the sintering techniques described herein.

As shown in step 1718, the method 1700 may include finishing the object,which may include cleaning, flushing, polishing, or otherwise finishingthe object and preparing the object for an intended use.

While the foregoing discussion expressly contemplates the removal ofmulti-part supporting structures from interior cavities, it will bereadily appreciated that the same or similar techniques may also orinstead be used to fabricate multi-part support structures for exteriorsurfaces of an object. This may be useful in numerous fabricationcontexts, such as where the support structures fully or partiallyenclose a fabricated object in a manner that creates mold lock—acondition where the object is mechanically locked or enclosed within anassociated support structure. In this context, a multi-part supportstructure may usefully be fabricated with non-sinterable interfaceregions in between so that the support structure can be easilydisassembled and removed after sintering (and infiltration whereapplicable) of the object into a densified part.

Thus, in one aspect, a method disclosed herein includes fabricating,from a first material, a support structure for an object, the supportstructure including two or more discrete support components; forming aninterface layer including a first portion of the interface layeradjacent to the support structure and a second portion of the interfacelayer between the two or more discrete support components; andfabricating a surface of the object from a second material, the surfaceof the object adjacent to the first portion of the interface layer andthe second material including a powdered material for forming a finalpart and a binder system including one or more binders, where the one ormore binders resist deformation of a net shape of the object duringprocessing of the object into the final part, where processing of theobject into the final part includes debinding the net shape to remove atleast a portion of the one or more binders and sintering the net shapeto join and densify the powdered material, and where the interface layerresists bonding of the support structure to the object during sintering.

The two or more discrete support components may, for example, be themodular support structures described above, configured for removal froman interior cavity, or the two or more discrete support components maybe exterior modular support structures that enclose the object, e.g., toform a locked mold about the object.

In another aspect, a method disclosed herein includes receiving such anarticle at a service bureau or the like for subsequent processing. Thus,the method may include receiving an article including a supportstructure fabricated from a first material, an object, and an interfacelayer, where the support structure includes two or more discrete supportcomponents for supporting an the object, where the interface layerincludes a first portion of the interface layer adjacent to the supportstructure and a second portion of the interface layer between the two ormore discrete support components, and where the object includes asurface fabricated from a second material including a powdered materialfor forming a final part and a binder system including one or morebinders, where the one or more binders resist deformation of a net shapeof the object during processing of the object into the final part, whereprocessing of the object into the final part includes sintering the netshape to join and densify the powdered material, and where the interfacelayer resists bonding of the support structure to the object duringsintering; and processing the article into the final part, whereprocessing the article includes at least one of debinding the articleand sintering the article, and where processing the article furtherincludes separating the object from the support structure at theinterface layer.

The support structure formed of the two or more discrete supportcomponents may, for example, include a print support for the object,e.g., that provides a surface for fabricated a layer of the objectthereupon. The two or more discrete support components may also orinstead include a debinding support for the object that resistsdeformation of the object during debinding. The support structure mayalso or instead include a sintering support for the object, e.g., thatresists slumping, fracturing, or other deformation of the object duringsintering into a final part.

Similarly, an article contemplated herein may include multiple, separatesupport structures separated by interface layers to facilitatedisassembly after sintering. Thus, an article contemplated hereinincludes an object formed of a build material, the build materialincluding a sinterable powdered material for forming a final part at asintering temperature, where the build material includes a binder systemcontaining one or more binders retaining the sinterable powderedmaterial in a net shape of the object prior to densifying the sinterablepowdered material into the final part; a support structure for theobject, the support structure positioned adjacent to a surface of theobject to provide mechanical support during at least one of printing theobject, debinding the object, and sintering the object, the supportstructure formed of one or more other materials having a shrinkage rateduring at least one of debinding and sintering coordinated with a secondshrinkage rate of the build material, where the support structureincludes two or more discrete components; and an interface layerdisposed between the support structure and the surface of the object andbetween each of the two or more discrete components of the supportstructure, the interface layer containing a composition that resistsbonding of the support structure to the surface of the object or otherones of the two or more discrete components through the interface layerduring sintering.

The support structure may for example form a locked mold enclosing theobject. In this context, the two or more discrete components may, whenseparated after sintering, disassemble to release the object from thelocked mold. In another aspect, the support structure may form aninterior support within a cavity of the object. In this interiorcontext, the two or more discrete components may, when separated aftersintering, disassemble for removal from the cavity.

FIG. 18 shows a flow chart of a method for forming an interface layer ina binder jetting process. Binder jetting techniques can be used todeposit and bind metallic particles or the like in a net shape fordebinding and sintering into a final part. Where support structures arerequired to mitigate deformation of the object during the debindingand/or sintering, an interface layer may usefully be formed between thesupport structures and portions of the object in order to avoid bondingof the support structure to the object during sintering.

As shown in step 1804, the method 1800 may begin with depositing layersof powdered material. This may, for example, include depositing a numberof layers of a powdered material in a bed such by spreading powderedmaterial in a powder bed as described above. The powdered material mayinclude a metallic powder or any other sinterable powder or the likeformed of a material selected for sintering into a final part. In orderto apply powder more quickly, depositing layers of powder may includeapplying successive layers of the powdered material in opposingdirections with a bi-directional spreader.

As shown in step 1806, the method 1800 may include applying a firstbinder to form a support. This may include applying a first binder in afirst pattern to the number of layers as they are deposited to form asupport structure from the powdered material within the bed.

As shown in step 1808, the method 1800 may include applying a secondbinder to form an object. For example, this may include applying asecond binder in a second pattern to the number of layers as they aredeposited to form an object from the powdered material within the bed.It will be appreciated that the support structure may be formed beneath,above, or vertically adjacent to the object, or some combination ofthese, according to the geometry of the object and any needed support.The first binder (for the support) and the second binder (for theobject) may be substantially similar or identical binder systemsdeposited from a single print head.

In one aspect, the second binder may usefully incorporate a secondaryinfiltrate selected to modify properties of a final part formed bysintering the object. For example, the secondary infiltrant may includeat least one of a carbon, a boron, and a metal salt to increase strengthof the object.

As shown in step 1810, the method 1800 may include applying an interfacematerial at an interface between the support structure and the object,where the interface material resists bonding of the support structure tothe object during sintering.

The interface material may, for example, include a colloidal suspensionof ceramic particles sized to infiltrate the sinterable powder in asurface of the support structure adjacent to the object. For example,where the sinterable powder used to form the object has a mean particlessize of about ten to thirty-five microns, the ceramic particles mayusefully have a mean particle size of less than one micron, or moregenerally at least one order of magnitude smaller than a similarlymeasure mean particle size of the sinterable powder. The interface layermay, for example, be applied by jetting the interface material through ajetting print head such as a binder jetting print head or any othersuitable print head or distribution mechanism.

The interface layer may also or instead include a layer of ceramicparticles deposited at a surface of the support structure adjacent tothe object. The layer of ceramic particles may be solidified to preventdisplacement by subsequent layers of the sinterable powder, therebyforming a sinter-resistant ceramic layer between the support structureand the object. For example, the layer of ceramic particles may bedeposited in a curable carrier, and the method 1800 may include curingthe curable carrier substantially concurrently with deposition on thesinterable powder.

In one aspect, the interface material, may include a material thatremains as an interface layer physically separating the supportstructure from the object after debind and into a thermal sinteringcycle. For example, an interface material may be deposited in anintermittent pattern between the support structure and the object tocreate a corresponding pattern of gaps between the support structure andthe object. If cured in these locations, a subsequent powder layer maybe displaced from locations carrying the interface material, with aresulting intermittent structure mechanically coupling the support tothe object. This configuration may effectively weaken a mechanicalstructure between the support structure and the object to facilitateremoval of the support structure, e.g., after debinding or sintering asappropriate, while retaining enough structure to provide the requiredsupport for printing, debinding, and/or sintering. The size and shape ofgaps between regions of interface material may depend, for example, onthe nature of the build materials and the debinding and sinteringprocess. But in general, any pattern may be used provided that thesupport and the object can retain their respective structure throughsubsequent processing.

Where the first binder used to form the support structure (or the secondbinder used to form the object) is debindable with a chemical solvent,the interface material may usefully be at least partially non-soluble inthe chemical solvent so that the interface material remains wholly orpartially intact through a chemical debind of the support structure(and/or the object).

In one aspect, the interface material may include a soluble metal saltthat transforms to a ceramic upon dehydration and heating. For example,the interface material may include at least one of a hydroxide, achloride, a sulfate, a nitrate, an acetate, and a stearate. Theinterface material may further include aluminum, and the interfacematerial may include at least one of zirconium, yttrium, silicon,titanium, iron, magnesium, and calcium.

In another aspect, the interface layer may be formed by jetting orotherwise depositing a solution that precipitates a non-sinteringmaterial. For example, aqueous solutions of aluminum sulfate, aluminumnitrate, aluminum triacetate, or zirconium acetate may be used. Othersalts of elements that form chemically resistant oxides upondecomposition may also or instead be used. Similarly, an interface layermay usefully be jetted as a polymer that decomposes into graphite(preferably where graphite is not strongly reactive with the buildmaterial of the object).

As shown in step 1814, the method may include debinding the object (andsupport structure, as appropriate) using any of the debinding techniquesdescribed herein.

As shown in step 1816, the method 1800 may include sintering the object(and support structure, as appropriate) in a thermal sintering cycleusing any of the sintering techniques described herein.

As shown in step 1818, the method 1800 may include finishing the object(and support structure, as appropriate) using any of the techniquesdescribed herein.

Objects, such as those made of a build material described herein, thatare processed through a sintering process may shrink in one or moredimensions. Objects are formed, such as through a three-dimensionalforming process described herein, from materials that are intended tofacilitate a consistent and controlled shrinkage so that an objectsubstantially maintains its formed shape. Forces, such as friction, canimpact one or more dimensions during the sintering process and thereforeresult in inconsistent shrinkage in the impacted dimensions. As anexample, an object placed on a setter during sintering may experiencefriction due to the relative movement of the object and the setter atthe sintering temperature. This may result in portions of the objectproximal to the setter shrinking at a different rate in a horizontaldirection compared to portions further away from the setter ordimensions other than horizontal. When forces, such as friction aremitigated, particularly along one of the dimensions of shrinkage, theresults of sintering may be improved so that a part more uniformlyshrinks; thereby maintaining its originally formed shape.

Techniques for reducing an impact of friction may include reducingfriction between an object and a sintering fixture and the like. Aninterface layer formed between an object and a sintering fixtureprovides a first level of friction reduction because the interface layermay resist bonding to the object and/or the sintering fixture. Thistechnique may be applied and extended to support structures that may beused to support an object through a sintering process. Rather thanforming a single interface layer below an object for sintering, a stackof layers, such as interface and support layers interleaved, may beformed to further mitigate an impact on a part resulting from frictionand the like. Forming interface layers that resist bonding interleavedwith support layers that provide physical support for a part beingformed may provide the necessary support for the object during sinteringwhile reducing friction impacting the object, such as along a bottomsurface of the object. A goal of such a stack may be to at leastpartially mechanically isolate the object that changes shape duringsintering from the sintering fixture (e.g., a base of a sintering ovenand the like). A greater number of layer pairs (support and interface)may provide greater mechanical isolation.

Multiple layer pairs may also facilitate isolating the object from anyof the support layer so that shrinkage of the support layers, which maybe formed of a sinterable material comparable to the object may occurwithout substantively impacting the object during sintering and thelike. In an example of a three layer-pair stack, an object may be formedatop the stack which may start with an interface layer at the top,followed by alternating support and interface layers. Each supportlayer, being mechanically isolated by the interface layers from othersupport layer(s) can therefore change size and/or shape during sinteringwithout substantively impacting an object sitting atop the stack.

In addition to forming a multi-layer support stack from any number ofinterleaved layers (support and interface layers), the shape anddimensions of each of the layers may vary. While a first embodiment ofsuch a stack may include each interface layer being substantiallyidentical and each support layer being substantially identical, otherembodiments may include a fixed number of layer pairs, but layerthickness, composition, shape (e.g., perimeter) and the like may vary.When two or more interface layers are formed, they may be formed ofdifferent thicknesses, such as to increase or decrease mechanicalisolation. An interface layer formed atop the stack, effectively belowan object to be sintered, may be a different thickness than an interfacelayer formed between two support layers. While material selection ofinterface layers may focus on resisting bonding, materials for each ofthe interface layers in such a stack may also be selected based on itsposition in the stack. In an example of stack position-influencedmaterial selection, a layer directly below an object may be formed of amaterial that affords greater freedom of movement of the part relativeto the next lower support layer. Such an object impacting layer may alsobe configured (e.g., material, thickness, shape, and the like) based onthe object being sintered. A heavier object may indicate a greaterthickness of this top interface layer. However, a heavier object mayalternatively indicate using a material that maintains it shape duringsintering independent of the location and weight of the object.

A shape of one or more layers of a multi-layer sintering supportstructure may also be influenced by a shape of an object. If the supportlayers of the structure are formed of the same, or substantially similarmaterial as the part, shrinkage rates may be comparable. Therefore,forming one or more of the layers to comply with a convex hullprojection of the object may facilitate more closely matching shrinkagerate and therefore overall shrinkage differences between the supportlayers of the stack and the object. This may further mitigate negativeeffects of friction because both parts shrink the same amount, at leastin one or more of the horizontal dimensions of the part. When a stack oftwo or more layer-pairs are formed to comply with a convex hullprojection of the part, the impacts of friction on shrinkage of theobject may be substantially diminished. This may be a result of lateralor horizontal shrinkage of the sinterable stack layers beingsubstantially similar to horizontal shrinkage of the object. This mayfurther be a result of the object and the sinterable stack layers havingthe same material composition.

An object that has a flat bottom surface may be placed upon a topinterface layer of a multi-layer sintering support structure, e.g., tofacilitate reducing an impact of friction on horizontal shrinkage of theobject through sintering temperature separation of the object from thesinterable layers of the support structure.

A multi-layer substrate for supporting an object during sintering may beformed between the object and any base support substrate that may beused to carry the object during fabrication into a final part.

Depending on the shape of an object for which a multi-layer substratemay be formed, an impact on shrinkage on the object due to differencesin shrinkage rate of the object and the substrate may be further reducedby creating a number of independent multi-layer substrates for differentcontact surfaces of the object. As described herein these independentmulti-layer substrates may be coupled to one another by tie bars,straps, or the like that are configured to shrink and that draw therafts toward one another in a manner that substantially matches theshrinkage of the object as debinding and sintering occurs.

While interface layers are generally depicted herein as discrete layers,it is understood that an interface layer may overlap with the object,extend beyond and/or overlap an adjacent support layer of a multi-layersubstrate, merge with another interface layer, and the like. Inembodiments, an interface layer may be comprised of a material thatincludes titanium. An interface layer may be formed of a compositionthat includes microsphere that controllably collapse under pressure toreduce volume, such as to facilitate separating the object from themulti-layer support structure/substrate.

FIG. 19 show a flow chart of a method for forming a multi-layer shrinkrate-isolating substrate that may be used as a support structure for asinterable object in a sintering process. A multi-layer shrinkrate-isolating substrate may be formed of a plurality of alternatinglayers that facilitate isolating an object going through the sinteringprocess from a sintering chamber fixtures, setter, or the like so thatfriction between the object and the chamber is mitigated during thesintering process.

As shown in step 1904, the method 1900 may begin with forming a baselayer of the substrate. Forming the base layer may include providing apowdered material that sinters at a sintering temperature. The powderedmaterial may be provided in a first shape. Forming the base layer mayfurther include providing a base layer comprising the powdered materialand a first binder system that facilitates retaining the first shape ofthe base layer. Forming the base layer may include fabricating the baselayer with a three-dimensional printer as described herein, such asaccording to a three-dimensional model.

As show in step 1906, the method 1900 may include fabricating a firstinterface layer of an interface material that resists sintering duringthermal processing at the sintering temperature. The first interfacelayer may be fabricated above the base layer with a three-dimensionalprinter by depositing, with the three-dimensional printer the interfacematerial atop the base layer.

As shown in step 1908, the method 1900 may include fabricating a supportlayer above the first interface layer. The support layer may befabricated from a material sinterable at the sintering temperature. Thesupport layer may be fabricated by depositing the sinterable materialwith a three-dimensional printer as described herein.

As shown in step 1910, the method 1900 may include depositing a secondinterface layer above the support layer. The second interface layer maycomprise the interface material. Depositing the second interface layermay include using a three-dimensional printer to form the secondinterface layer atop the support layer. In embodiments, the first andsecond interface layers may reduce to powder during thermal processingat the sintering temperature. The first interface layer may resistbonding of the base layer to the support layer during thermal processingat the sintering temperature. In embodiments, one or more of the firstor second interface layers may comprise a ceramic powder that has asintering temperature substantially higher than the sinteringtemperature of the base or support layers.

As shown in step 1912, the method 1900 may include fabricating an objectabove the second interface layer. Fabricating the object may includefabricating the object from a build material that may include a powderedmetal that sinters at the sintering temperature and a second bindersystem that retains a second shape of the object, such as the shape intowhich the object is fabricated, during processing of the object into afinal part. Fabricating the object may include depositing the buildmaterial with a three-dimensional printer according to athree-dimensional model. The build material may have substantiallysimilar composition to the base layer, the support layer and the like.The build material may have a substantially similar sintering shrinkagerate to the base layer, the support layer and the like.

The method 1900 for forming a multi-layer shrink rate-isolatingsubstrate may include fabricating additional layer pairs, such as one ormore additional support layer and one or more additional interfacelayers between the base layer and the object so that, for example, thestructure may include a base layer, three interface layers, and twointervening support layers. In embodiments, three or more sets ofinterface and support layers may also be formed between the base layerand the object.

FIG. 20 shows a diagram of an embodiment of a structure 2000 forsintering an object, the structure 2000 configured to, among otherthings, facilitate mitigating impacts of friction on the object during asintering process. The structure may substantially reduce frictionbetween, for example, a portion of a chamber on which the structurerests and the object during the sintering process. The structure mayinclude a plurality of interleaved layers of sinterable material andinterface material that resists bonding to the sinterable materiallayers, thereby allowing at least the individual sinterable layers tochange shape during sintering with greater independence of shape changesoccurring to other sinterable layers. The result may be a structure thatsignificantly reduces an impact of friction, such as friction inhorizontal directions, on the object during sintering.

As shown, the structure 2000 may include an object 2002 fabricated froma first material, such as depositing a build material with athree-dimensional printer. The object may be fabricated according to athree-dimensional model of the object. The first material for thisobject may include a sinterable powder and a binder that facilitatesretaining a shape of the object during processing into a final part.

As shown, the structure 2000 may include a plurality of sinterablelayers represented by elements 2004, 2004′ that may be formed of asinterable material. The sinterable material may have a shrink rate thatsubstantially matches a shrink rate of the object. The sinterable layermaterial shrink rate may match the shrink rate of the first material.

As show, the structure 2000 may include a plurality of interface layersrepresented by elements 2008 and 2008′ that may resist sintering at asintering temperature for the sinterable powder of the first material.The interface layers may resist sintering at processing temperatureswell above a sintering temperature for the sinterable powder of thefirst material.

As shown, the sinterable layers 2004, 2004′ and the interface layers2008, 2008′ may be alternated to form a vertical stack of substantiallyparallel layers. The stack may be configured so that a sinterable layer2004 is at the bottom of the stack; an interface layer 2008 is disposedatop the sinterable layer 2004; a second sinterable layer 2004′ isdisposed atop the interface layer 2008; and an interface layer 2008′ isat the top of the stack. The object may be fabricated atop the interfacelayer 2008′ at the top of the stack. In embodiments, an additionalinterface layer may be formed below the sinterable layer 2004, therebyforming a stack with an interface layer at the bottom.

As shown the structure 2000 may comprise the object 2002 and a verticalstack of interleaved layers 2004, 2008, 2004′ and 2008′, wherein thestack perimeter may be consistent with a projected convex hull of theobject 2002. The stack perimeter may be based on the projected convexhull of the object 2002 but may include some additional margin forstability of the object during processing.

While interface layers generally share a common property of resistingbonding to adjacent sinterable layers, the interface layer 2008 may beformed from a material having a different composition than the interfacelayer 2008′. In embodiments with more than two interface layers, one ormore of the interface layer may be formed of a different compositionthan the other interface layers. In embodiments, one or more of theinterface layers may comprise a ceramic powder that has a sinteringtemperature substantially higher than the sintering temperature of thesinterable layers.

Layers in the structure 2000 may be formed into different thicknesses.The sintering layers may be substantially thicker than the interfacelayers. In embodiments, one or more of the sintering layers may be atleast three times greater in thickness than any one of the interfacelayers.

FIG. 21 shows a diagram of an embodiment of a structure 2100 forsintering an object, the structure configured to facilitate mitigatingimpacts of friction on the object during a sintering process. Thestructure may substantially reduce friction between, for example, aportion of a chamber on which the structure rests and the object duringthe sintering process. The structure may include a plurality of supportlayers formed from a powdered material that sinters at a sinteringtemperature into a densified layer that may shrink during sintering. Thestructure may include a plurality of interface layers disposed so thatat least one of the interface layers is positioned between two supportlayers. Each interface layer may be formed from a material that preventsbonding between the two adjacent support layers, such as when thestructure is processed at a sintering temperature. The structure mayfurther include a top layer that may be formed of the material thatprevents bonding as described above. The top layer may include a layerof the material from which each interface layer is formed.

As shown, the structure 2100 may further include an object 2102fabricated from a first material, such as with a three-dimensionalprinter. The object may be fabricated according to a three-dimensionalmodel of the object. The first material for this object may include asinterable powder and a binder that facilitates retaining a shape of theobject during processing into a final part. The object and at least oneof the support layers may comprise the same powder and binder.

As shown, the support layers, represented by for example, elements 2104and 2104′ that may be formed to substantially match asintering-initiated shrink rate of the object 2102. As show, theinterface layers, represented by elements 2008 and 2008′ may resistsintering at a sintering temperature of the object 2102. The interfacelayers may comprise a material that resists bonding at a significantlyhigher temperature than a sintering temperature of the object 2100 oreither of the support layers 2104, 2104′.

As shown, the layers may be arranged to form a vertical stack. The stackmay be configured so that a support layer 2104 is at the bottom of thestack; an interface layer 2108 is disposed atop the support layer 2104;a second support layer 2104′ is disposed atop the interface layer 2108;and a top layer 2110 is at the top of the stack. The object 2100 may befabricated atop the stack. The layers in the vertical stack may beconfigured to extend beyond the perimeter of the object in one or morehorizontal directions. An additional interface layer, not shown, may beformed below the lower-most support layer 2104.

As shown an additional feature of the structure may include a network ofopen passages 2112. This network may further improve a sintering processby, for example facilitating drainage of a debinding solution from thestructure.

The above systems, devices, methods, processes, and the like may berealized in hardware, software, or any combination of these suitable fora particular application. The hardware may include a general-purposecomputer and/or dedicated computing device. This includes realization inone or more microprocessors, microcontrollers, embeddedmicrocontrollers, programmable digital signal processors or otherprogrammable devices or processing circuitry, along with internal and/orexternal memory. This may also, or instead, include one or moreapplication specific integrated circuits, programmable gate arrays,programmable array logic components, or any other device or devices thatmay be configured to process electronic signals. It will further beappreciated that a realization of the processes or devices describedabove may include computer-executable code created using a structuredprogramming language such as C, an object oriented programming languagesuch as C++, or any other high-level or low-level programming language(including assembly languages, hardware description languages, anddatabase programming languages and technologies) that may be stored,compiled or interpreted to run on one of the above devices, as well asheterogeneous combinations of processors, processor architectures, orcombinations of different hardware and software. In another aspect, themethods may be embodied in systems that perform the steps thereof, andmay be distributed across devices in a number of ways. At the same time,processing may be distributed across devices such as the various systemsdescribed above, or all of the functionality may be integrated into adedicated, standalone device or other hardware. In another aspect, meansfor performing the steps associated with the processes described abovemay include any of the hardware and/or software described above. Allsuch permutations and combinations are intended to fall within the scopeof the present disclosure.

Embodiments disclosed herein may include computer program productscomprising computer-executable code or computer-usable code that, whenexecuting on one or more computing devices, performs any and/or all ofthe steps thereof. The code may be stored in a non-transitory fashion ina computer memory, which may be a memory from which the program executes(such as random-access memory associated with a processor), or a storagedevice such as a disk drive, flash memory or any other optical,electromagnetic, magnetic, infrared or other device or combination ofdevices. In another aspect, any of the systems and methods describedabove may be embodied in any suitable transmission or propagation mediumcarrying computer-executable code and/or any inputs or outputs fromsame.

The method steps of the implementations described herein are intended toinclude any suitable method of causing such method steps to beperformed, consistent with the patentability of the following claims,unless a different meaning is expressly provided or otherwise clear fromthe context. So, for example, performing the step of X includes anysuitable method for causing another party such as a remote user, aremote processing resource (e.g., a server or cloud computer) or amachine to perform the step of X. Similarly, performing steps X, Y and Zmay include any method of directing or controlling any combination ofsuch other individuals or resources to perform steps X, Y and Z toobtain the benefit of such steps. Thus, method steps of theimplementations described herein are intended to include any suitablemethod of causing one or more other parties or entities to perform thesteps, consistent with the patentability of the following claims, unlessa different meaning is expressly provided or otherwise clear from thecontext. Such parties or entities need not be under the direction orcontrol of any other party or entity, and need not be located within aparticular jurisdiction.

It will be appreciated that the methods and systems described above areset forth by way of example and not of limitation. Numerous variations,additions, omissions, and other modifications will be apparent to one ofordinary skill in the art. In addition, the order or presentation ofmethod steps in the description and drawings above is not intended torequire this order of performing the recited steps unless a particularorder is expressly required or otherwise clear from the context. Thus,while particular embodiments have been shown and described, it will beapparent to those skilled in the art that various changes andmodifications in form and details may be made therein without departingfrom the spirit and scope of this disclosure and are intended to form apart of the invention as defined by the following claims, which are tobe interpreted in the broadest sense allowable by law.

1-20. (canceled)
 21. A method for additive manufacturing, the methodcomprising: depositing a first amount of a first metal build materialhaving a first sintering temperature; depositing a first amount ofinterface material on a surface of the first amount of the first metalbuild material, the interface material having a second sinteringtemperature greater than the first sintering temperature; depositing asecond amount of the first metal build material on a surface of thefirst amount of interface material; and depositing a second amount ofinterface material on a surface of the second amount of the first metalbuild material, wherein the first amount of interface materialphysically separates the first amount of the first metal build materialfrom the second amount of the first metal build material
 22. The methodaccording to claim 21, wherein the depositing the first amount of metalbuild material, the first amount of interface material, the secondamount of metal build material, and the second amount of interfacematerial includes forming a plurality of gaps where the first amount ofmetal build material, the first amount of interface material, the secondamount of metal build material, and the second amount of interfacematerial are not deposited, and wherein each gap from the plurality ofgaps overlaps at least one adjacent gap from the plurality of gaps in atleast one of a vertical direction or a horizontal direction.
 23. Themethod according to claim 21, further comprising printing athree-dimensional (3D) object on a surface of the second amount ofinterface material using a second metal build material.
 24. The methodaccording to claim 23, wherein the second metal build material is thesame as the first metal build material.
 25. The method according toclaim 23, wherein the metal build material includes a binder, andwherein the method further comprises: de-binding a first portion of thebinder; and heating the first amount of the first metal build material,the second amount of metal build material, and the 3D object, wherein asecond portion of the binder is vaporized during the heating step. 26.The method according to claim 23, further comprising heating the firstamount of the first metal build material, the second amount of the firstmetal build material, the first amount of interface material, the secondamount of interface material, and the 3D object to the first sinteringtemperature, wherein a volume of each of the first amount of the firstmetal build material, the second amount of the first metal buildmaterial, and the 3D object decreases during the heating.
 27. The methodaccording to claim 23, wherein the first metal build material has afirst physical property and the second metal build material also has thefirst physical property.
 28. The method according to claim 21, furthercomprising depositing an initial amount of interface material beforedepositing the first amount of the first metal build material.
 29. Themethod according to claim 21, wherein the interface material issinter-resistant to the first metal build material when heated to thefirst sintering temperature.
 30. The method according to claim 21,further comprising depositing amounts of a support material to form oneor more supports, wherein the support material forming the one or moresupports has a different shrink ratio than a shrink ratio of the firstmetal build material.
 31. The method according to claim 21, wherein oneor more of the first amount of the first metal build material or thesecond amount of the first metal build material are formed of aplurality of layers of the first metal build material, and one or moreof the first amount of interface material or the second amount ofinterface material are formed of a plurality of layers of the interfacematerial.
 32. The method according to claim 21, wherein the methodfurther comprises depositing the first amount of the first metal buildmaterial on a printing surface and controlling a temperature of theprinting surface.
 33. The method according to claim 21, wherein thefirst amount of the first metal build material is deposited on aprinting surface, and wherein the method further comprises moving theprinting surface.
 34. The method according to claim 21, wherein theinterface material includes a ceramic material.
 35. A method of printinga three-dimensional (3D) object, the method comprising: forming aplurality of layers on a build surface, wherein each of the plurality oflayers includes a first material including metal powder; depositing aninterface layer including a second material on a surface of a topmostlayer of the plurality of layers and on at least another layer of theplurality of layers; and forming the 3D object out of the firstmaterial, wherein the 3D object is formed on the interface layerdeposited on the topmost layer of the plurality of layers.
 36. Themethod according to claim 35, wherein the forming the plurality oflayers includes forming a plurality of gaps where the first materialfrom each of the plurality layers is not formed, and wherein theplurality of gaps in each layer of the plurality of layers overlaps withthe plurality of gaps on adjacent layers of the plurality of layers. 37.A method of printing a three-dimensional (3D) object, the methodcomprising: forming a plurality of layers on a build surface, whereineach layer of the plurality of layers includes a first material;depositing an interface layer including a second material on a surfaceof a topmost layer of the plurality of layers and on at least anotherlayer of the plurality of layers; and printing the 3D object out of athird material, wherein the 3D object is printed on the interface layerdeposited on the topmost layer of the plurality of layers, wherein thefirst material and the third material each have a sintering temperaturethat is below a sintering temperature of the second material.
 38. Themethod according to claim 37, wherein the first material and the thirdmaterial each include a metal powder.
 39. The method according to claim38, wherein the metal powder of the first material is the same as themetal powder of the second material.
 40. The method according to claim37, wherein the metal powder of the first material has a first physicalproperty and a metal powder in the third material also has the firstphysical property.